Slough, U.K., May 18, 2004 (PRIMEZONE) -- Celltech Group plc


      --   Celltech's shareholders to receive 550 pence per
           ordinary share (equivalent to USD 19.44 per American
           Depositary Share) valuing the entire issued share
           capital of Celltech at GBP 1,530 million
      --   Celltech Board unanimously recommends the Offer
      --   Combination of UCB and Celltech to create a
           biopharmaceutical leader, based on strong and innovative
           R&D and a global platform for product commercialisation
      --   Blending of complementary skills and strong cultural fit
           to deliver outstanding growth

Summary


  --   The boards of UCB S.A. ("UCB") and Celltech Group plc
       ("Celltech" or the "Company") announce that they have agreed
       the terms of a recommended cash offer by UCB for the entire
       issued and to be issued share capital of Celltech either in
       the form of Celltech Shares or Celltech ADSs.

  --   The Celltech Board, which has been so advised by Morgan
       Stanley & Co. Limited ("Morgan Stanley") and J.P. Morgan plc
       ("JPMorgan"), considers the terms of the offer (the "Offer")
       to be fair and reasonable. In providing advice to the
       Celltech Board, Morgan Stanley and JPMorgan have taken into
       account the commercial assessments of the Celltech Board.
       Accordingly, the Celltech Board unanimously intends to
       recommend that Celltech Shareholders accept the Offer.

  --   The Offer for each Celltech Share will be 550 pence in cash
       and the Offer for each Celltech ADS will be 1,100 pence,
       equivalent to USD 19.44, in cash. The Offer will value the
       existing issued share capital of Celltech at approximately
       GBP 1,530 million.

  --   The Offer will represent a premium of approximately:

       --         27.8 per cent. to the
                  middle-market closing price
                  of 430.5 pence per Celltech
                  Share on 17 May 2004, the
                  last business day prior to
                  the date of this
                  announcement;

       --         26.3 per cent. to the average
                  middle-market closing price
                  of 435.6 pence per Celltech
                  Share during the three months
                  prior to 17 May 2004; and

       --         44.7 per cent. to the average
                  middle-market closing price
                  of 380.1 pence per Celltech
                  Share during the twelve
                  months prior to 17 May 2004.

  --   UCB will finance the acquisition through bank loans. It is
       expected that the transaction will be earnings accretive,
       post synergies and before goodwill and other intangibles
       amortisation, after the second full year.

  --   Directors of Celltech and certain members of their immediate
       families have irrevocably undertaken to accept the Offer in
       respect of the Celltech Shares that they beneficially own
       and control, representing approximately 0.18 per cent. of
       the existing issued share capital of Celltech.

  --   UCB, headquartered in Brussels, had a turnover of
       approximately Euro 3 billion in 2003 and employs over 11,500
       people. Its flagship pharmaceutical business had a turnover
       of Euro 1.5 billion and an EBIT of Euro 397 million in 2003.
       Its pharmaceutical research activities employ over 1,000
       people and have a budget of Euro 244 million for 2004.

  --   Celltech is a leading UK based biotech company which employs
       some 1,900 people and had turnover in excess of GBP 350
       million in 2003. Its investment in R&D activity, which
       employs some 450 people, amounted to GBP 106 million in
       2003. Operating profit pre exceptional items and goodwill
       amounted to approximately GBP 50 million in 2003. Celltech
       has a broad and innovative pipeline including a major new
       product in advanced phase III trials (CDP870) for which UCB
       has entered into a worldwide license agreement. The license
       agreement is not conditional upon the success of the
       proposed Offer for Celltech by UCB.

  --   The combination of UCB and Celltech will create a European
       based company which will be one of the largest
       biopharmaceutical companies in the world. In a number of
       important areas the combined group will benefit from a high
       degree of complementarity:

       --         Complementary product
                  offerings: the combined group
                  will have strong positions in
                  specialty therapeutic areas
                  such as Central Nervous
                  System (Epilepsy, Multiple
                  Sclerosis, Parkinson's
                  Disease, etc.), Inflammation
                  (Respiratory, Rheumatology,
                  Gastro-Enterology) and
                  Oncology;

       --         Strengthened research and
                  development: the combined
                  group will benefit from
                  Celltech's innovative
                  expertise in biotechnological
                  R&D, especially monoclonal
                  antibodies, and UCB's
                  expertise in pharmaceutical
                  chemistry. This will result
                  in a significantly
                  strengthened combination of
                  small and large molecule
                  discovery and development
                  expertise allowing the
                  combined group to increase
                  the flow of drug development
                  candidates;

       --         Stronger and broader
                  commercial operations (US,
                  Europe and Asia): the
                  combined group will be better
                  positioned, through its
                  enhanced global presence, to
                  commercialise and launch new
                  products, particularly in the
                  specialist areas in which the
                  combination will focus and
                  where UCB has already
                  demonstrated its ability to
                  launch and propel products
                  successfully to market
                  leadership (e.g., Keppra);
                  and

       --         The blending of skills and
                  culture, through the
                  successful combination of
                  competencies at all levels of
                  the combined entity, will
                  accelerate innovation and
                  profitable growth.

  --   A Loan Note Alternative will also be made available to
       Celltech Shareholders other than certain Overseas Celltech
       Shareholders.

Commenting on the Offer, Dr. Peter Fellner, Chairman of Celltech, said:

"Since listing in 1993, Celltech has successfully established itself as one of Europe's leading biotechnology companies built on a platform of internationally respected research and excellent people. UCB recognises these strengths and this offer represents fair value for Celltech Shareholders."

Commenting on the Offer, Baron Georges Jacobs, Chairman of the Executive Committee of UCB, said:

"We have pursued and implemented over the last few years an ambitious plan to develop the company in pharmaceuticals, including through external growth. I am therefore very pleased to announce this transaction which represents a major step in the implementation of our goals, as well as a unique opportunity to build a leading innovative biopharmaceutical company."

Commenting on the Offer, Dr. Goran Ando, CEO of Celltech said:

"Celltech possesses unique and outstanding UK based research capabilities which UCB has committed to making a cornerstone of the combined group's growth strategy. Together, we will be one of the world's largest biopharmaceutical companies."

Commenting on the Offer, Roch Doliveux, CEO of UCB Pharma said:

"I am looking forward to working with Celltech's excellent management and fine scientific teams to transform Celltech's and UCB's very promising pipeline into commercial value for our shareholders. The new combined entity has all that it takes to rapidly be positioned as a global leader in Neurology, especially with Keppra and its successors, in Inflammation with CDP870, and in Allergy with Xyzal and Zyrtec, with a strong research engine focused on validated targets to fuel our long term growth."

Lazard & Co., Limited ("Lazard") is acting as exclusive financial adviser to UCB in relation to the Offer. Morgan Stanley and JPMorgan are acting as financial advisers to Celltech in relation to the Offer. Lazard Freres & Co. LLC is acting as dealer manager for the Offer in the United States.

In connection with the Offer, Panmure Gordon, a division of Lazard is acting as broker to UCB.

This summary should be read in conjunction with the full text of the following announcement. Appendix III to the following announcement contains definitions of certain terms used in this summary and the following announcement.

There will be a presentation to analysts at 09:00 BST today in the Great Hall at JPMorgan, 60 Victoria Embankment, London, EC4Y OJP and at 16:30 CET at UCB, 60 Allee de la Recherche, 1070 Brussels.

Interviews with Georges Jacobs, Chairman of the Executive Committee of UCB, Dr. Roch Doliveux, CEO of UCB Pharma, and Dr. Goran Ando, CEO of Celltech, are available on www.cantos.com and www.celltechgroup.com.

Lazard is acting for UCB and no one else in connection with the Offer and will not be responsible to anyone other than UCB for providing the protections afforded to clients of Lazard or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

Morgan Stanley is acting for Celltech and no one else in connection with the Offer and will not be responsible to anyone other than Celltech for providing the protections afforded to clients of Morgan Stanley or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

JPMorgan is acting for Celltech and no one else in connection with the Offer and will not be responsible to anyone other than Celltech for providing the protections afforded to clients of JPMorgan or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

This press announcement does not constitute an offer or invitation to purchase any securities or a solicitation of an offer to buy any securities, pursuant to the Offer or otherwise. The Offer will be made solely by means of an Offer Document and the Acceptance Forms accompanying the Offer Document, which will contain the full terms and conditions of the Offer, including details of how the Offer may be accepted. In the United States, UCB will file a Tender Offer Statement containing the Offer Document and other related documentation with the US Securities and Exchange Commission (the "SEC") on Schedule TO and Celltech will file a Solicitation/Recommendation Statement with the SEC on Schedule 14D-9 on the date the Offer Document is mailed to Celltech Shareholders. Free copies of the Schedule TO, the Schedule 14D-9 and the other related documents to be filed by Celltech or UCB in connection with this Offer will be available from the date the Offer Document is mailed to Celltech Shareholders on the SEC's website at http://www.sec.gov. The Offer Document and Acceptance Forms accompanying the Offer Document will be made available to all Celltech Shareholders at no charge to them. Celltech Shareholders are advised to read the Offer Document and the accompanying Acceptance Forms when they are sent to them because they will contain important information. Celltech Shareholders in the United States are also advised to read the Tender Offer Statement and the Solicitation/Recommendation Statement because they will contain important information.

It should be noted that by virtue of the conflicting provisions of the City Code and the Exchange Act, the Panel has agreed that the Acceptance Condition can be structured so that the Offer cannot become or be declared unconditional as to acceptances until such time as all other conditions of the Offer have been satisfied, fulfilled or, to the extent permitted, waived. The Acceptance Condition in paragraph (a) of Appendix I has been amended accordingly.

Unless otherwise determined by UCB and permitted by applicable law and regulation, the Offer (including the Loan Note Alternative) will not be made, directly or indirectly, in or into, or by use of the mails of, or by any other means or instrumentality (including, without limitation, telephonically or electronically) of interstate or foreign commerce of, or of any facility of a national securities exchange of Canada, nor will it be made in or into Belgium, Australia or Japan and the Offer will not be capable of acceptance by any such use, means, instrumentality or facilities or from within Belgium, Australia, Canada or Japan. Accordingly, unless otherwise determined by UCB and permitted by applicable law and regulation, neither copies of this announcement nor any other documents relating to the Offer are being, or may be, mailed or otherwise forwarded, distributed or sent in or into Belgium, Australia, Canada or Japan and persons receiving such documents (including custodians, nominees and trustees) must not distribute or send them in, into or from such jurisdictions.

The Loan Notes to be issued pursuant to the Loan Note Alternative have not been, and will not be, listed on any stock exchange and have not been and will not be registered under the Securities Act or under any relevant securities laws of any state or other jurisdiction of the United States, or under the relevant securities laws of Belgium, Australia, Canada or Japan or any other jurisdiction. Accordingly, unless an exemption under such relevant laws is available, Loan Notes may not be offered, sold, re-sold or delivered, directly or indirectly, in, into or from the United States, Belgium, Australia, Canada or Japan or any other jurisdiction in which an offer of Loan Notes would constitute a violation of relevant laws or require registration of the Loan Notes, or to or for the account or benefit of any US person or resident of Belgium, Australia, Canada or Japan or any other such jurisdiction.

The Panel wishes to draw the attention of member firms of the New York Stock Exchange to certain UK dealing disclosure requirements during the offer period. The offer period (in accordance with the City Code, which is published and administered by the Panel) commences at the time when an announcement is made of a proposed or possible offer, with or without terms. Celltech has equity securities traded on the London Stock Exchange and the New York Stock Exchange.

The above disclosure requirements are set out in more detail in Rule 8 of the City Code. In particular, Rule 8 requires public disclosure of dealings during the offer period by persons who own or control, or who would as a result of any transaction own or control, one per cent. or more of any class of relevant securities of the offeree company. Relevant securities include Celltech Shares, Celltech ADSs, instruments convertible into Celltech Shares or Celltech ADSs and options in respect of any of the foregoing and derivatives referenced to any of the foregoing. This requirement will apply until the first closing date or, if this is later, the date when the Offer becomes or is declared unconditional or lapses.

Disclosure should be made on an appropriate form by no later than 12:00 noon (London time), 7:00 a.m. (New York City time), on the business day following the date of the dealing transaction. These disclosures should be sent a Regulatory Information Service and a copy faxed to the Panel (+44 (0) 20 7638 1554).

The Panel requests that member firms advise those of their clients who wish to deal in the relevant securities of Celltech, whether in the United States or in the United Kingdom, that they may be affected by these requirements. If there is any doubt as to their application the Panel should be consulted (telephone number: +44 (0) 20 7382 9026, fax number: +44 (0) 20 7638 1554).

This press announcement includes "forward-looking statements" relating to the Offer, UCB and Celltech that are subject to known and unknown risks and uncertainties, many of which are outside of UCB's and Celltech's control and are difficult to predict, that may cause actual results to differ materially from any future results expressed or implied from such forward-looking statements. Important factors that could cause actual results to differ materially from such expectations include, without limitation: the inability to obtain necessary regulatory approvals in the context of the Offer or to obtain them on acceptable terms; the inability to integrate successfully Celltech within UCB or to realise synergies from such integration following the acquisition; costs related to the acquisition of Celltech; the economic environment of the industries in which UCB and Celltech operate; costs associated with research and development; changes in the prospects for products in the research and development pipeline of UCB or Celltech; dependence on the existing management of UCB and Celltech; changes or uncertainties in UK or US federal or state tax laws or the administration of such laws; changes or uncertainties in the laws or regulations applicable to the markets in which UCB and Celltech operate, including those of the Federal Drug Administration in the United States; and other factors detailed in Celltech's filings with the SEC.


  1.       Introduction

           The boards of UCB and Celltech announce that they have
           agreed the terms of a recommended cash offer, to be made
           by UCB, and outside the United States, by Lazard on its
           behalf, for the entire issued and to be issued share
           capital of Celltech either in the form of Celltech
           Shares or Celltech ADSs. The Offer for each Celltech
           Share will be 550 pence in cash. This represents 1,100
           pence for each Celltech ADS (each Celltech ADS
           representing two Celltech Shares). The Offer will value
           the existing issued share capital of Celltech at
           approximately GBP 1,530 million.

           The Celltech Board, which has been so advised by Morgan
           Stanley and JPMorgan, considers the terms of the Offer
           to be fair and reasonable. In providing advice to the
           Celltech Board, Morgan Stanley and JPMorgan have taken
           into account the commercial assessments of the Celltech
           Board. Accordingly, the Celltech Board unanimously
           intends to recommend that Celltech Shareholders accept
           the Offer.

           Directors of Celltech and certain members of their
           immediate families have irrevocably undertaken to accept
           the Offer in respect of the Celltech Shares that they
           beneficially own and control, amounting in aggregate to
           493,029 Celltech Shares, representing approximately 0.18
           per cent. of the existing issued share capital of
           Celltech.

           Lazard is acting as exclusive financial adviser to UCB
           in relation to the Offer. Morgan Stanley and JPMorgan
           are acting as financial advisers to Celltech in relation
           to the Offer.

  2.       The Offer

           UCB and (outside of the United States) Lazard, on behalf
           of UCB, will offer to acquire, on the terms and subject
           to the conditions set out below and in Appendix I of
           this announcement, and to be set out in the Offer
           Document and the Acceptance Forms, all of the Celltech
           Shares and Celltech ADSs.

           The Offer will be made on the following basis:


              for each Celltech Share     550 pence in cash

              for each Celltech ADS       1,100 pence (equivalent to
                                          USD 19.44) in cash

           The Offer will value the existing issued share capital
           of Celltech at approximately GBP 1,530 million.

           The Offer will represent a premium of approximately:

           --   27.8 per cent. to
                the middle-market
                closing price of
                430.5 pence per
                Celltech Share on
                17 May 2004, the
                last business day
                prior to the date
                of this
                announcement;

           --   26.3 per cent. to
                the average
                middle-market
                closing price of
                435.6 pence per
                Celltech Share
                during the three
                months prior to
                17 May 2004; and

           --   44.7 per cent. to
                the average
                middle-market
                closing price of
                380.1 pence per
                Celltech Share
                during the twelve
                months prior to
                17 May 2004.

           The Celltech Shares (including those represented by
           Celltech ADSs) will be acquired pursuant to the Offer
           fully paid and free from all liens, charges, equitable
           interests, encumbrances, rights of pre-emption and any
           other rights and interests of any nature whatsoever and
           together with all rights now and hereafter attaching
           thereto, including voting rights and the right to
           receive and retain in full all dividends and other
           distributions (if any) declared, made or paid on or
           after the date of this announcement.

           The Offer Document will be sent to Celltech Shareholders
           shortly. The Offer will be on the terms and will be
           subject to the conditions which are set out in Appendix
           I and to those terms which will be set out in the Offer
           Document and in the accompanying Acceptance Forms, and
           such further terms as may be required to comply with the
           rules and regulations of the Financial Services
           Authority, the United Kingdom Listing Authority, The
           London Stock Exchange and with the City Code and US
           federal securities laws (except to the extent of any
           exemptive relief granted by the SEC).

  3.       Loan Note Alternative

           Celltech Shareholders (other than certain Overseas
           Celltech Shareholders, including Celltech Shareholders
           in the United States) who validly accept the Offer will
           be entitled to elect to receive Loan Notes to be issued
           by UCB instead of some or all of the cash consideration
           to which they would otherwise be entitled pursuant to
           the Offer.

           The Loan Note Alternative will be made available on the
           following basis:

             for every whole GBP 1 in cash    GBP 1 nominal value of
             consideration                    Loan Notes


           The Loan Notes, which will be governed by English law,
           will be unsecured and will be issued credited as fully
           paid in amounts and integral multiples of GBP 1 nominal
           value. All fractional entitlements to the Loan Notes
           will be disregarded. No application will be made for the
           Loan Notes to be listed or dealt in on any stock
           exchange.

           The Loan Notes will bear interest at 0.75 per cent.
           below six-month sterling LIBOR. Interest will be payable
           by six-monthly instalments in arrears (less any tax
           required to be withheld) on 31 March and 30 September in
           each year. The first payment of interest will be made on
           31 March 2005 (the "First Payment Date"). On the First
           Payment Date, interest will be paid in respect of the
           period from (and including) the first date of issue of
           the Loan Notes to (but excluding) the First Payment
           Date. The Loan Notes will be redeemable in whole or in
           part for cash at the option of noteholders on 31 March
           2005 and on subsequent interest payment dates. In
           certain circumstances, UCB will have the right to redeem
           all of the Loan Notes. If not previously redeemed, all
           outstanding Loan Notes will be redeemed on 30 September
           2010.

           No Loan Notes will be issued unless, on or before the
           date on which the Offer becomes or is declared
           unconditional in all respects, valid elections have been
           received in respect of at least GBP 5 million in nominal
           value of Loan Notes. If insufficient elections are
           received, Celltech Shareholders electing for the Loan
           Note Alternative will instead receive cash in accordance
           with the terms of the Offer.

           Subject as aforesaid, the Loan Note Alternative will
           remain open for acceptance for so long as the Offer
           remains open for acceptance. The Loan Note Alternative
           will be conditional upon the Offer becoming or being
           declared unconditional in all respects.

           Celltech Shareholders and holders of Celltech ADSs who
           are not resident in the United Kingdom should refer to
           paragraph 14 below.

           Further details of the Loan Notes will be contained in
           the Offer Document.

  4.       Irrevocable Undertakings to accept the Offer

           UCB has received irrevocable undertakings to accept the
           Offer from Directors of Celltech and certain members of
           their immediate families in respect of, in aggregate,
           493,029 Celltech Shares, representing all of the
           Celltech Shares beneficially owned and controlled by the
           Directors and such family members. This represents
           approximately 0.18 per cent. of the existing issued
           share capital of Celltech. Such undertakings cease to be
           binding only if the Offer lapses or is withdrawn.

  5.       Background to and reasons for the Offer

           The combination of UCB and Celltech will create a
           European based company which will be one of the largest
           biopharmaceutical companies in the world. In a number of
           important areas the combined group will benefit from a
           high degree of complementarity:

           --               Complementary product offerings: the
                            combined group will have strong
                            positions in specialty therapeutic
                            areas such as Central Nervous System
                            (Epilepsy, Multiple Sclerosis,
                            Parkinson's Disease, etc.),
                            Inflammation (Respiratory,
                            Rheumatology, Gastro-Enterology) and
                            Oncology;

           --               Strengthened research and development:
                            the combined group will benefit from
                            Celltech's innovative expertise in
                            biotechnological R&D, especially
                            monoclonal antibodies, and UCB's
                            expertise in pharmaceutical chemistry.
                            This will result in a significantly
                            strengthened combination of small and
                            large molecule discovery and
                            development expertise allowing the
                            combined group to increase the flow of
                            drug development candidates;

           --               Stronger and broader commercial
                            operations (US, Europe and Asia): the
                            combined group will be better
                            positioned, through its enhanced global
                            presence, to commercialise and launch
                            new products, particularly in the
                            specialist areas in which the
                            combination will focus and where UCB
                            has already demonstrated its ability to
                            launch and propel products successfully
                            to market leadership (e.g., Keppra);
                            and

           --               The blending of skills and culture,
                            through the successful combination of
                            competencies at all levels of the
                            combined entity, will accelerate
                            innovation and profitable growth.

           The combined R&D operations of the Group will have their
           headquarters in Slough, UK.

           Dr. Goran Ando will be deputy CEO of the combined group
           and Peter Allen will be in charge of integration.

           As separately announced today, UCB and Celltech have
           entered into a co-exclusive worldwide collaboration
           agreement for the research, development and
           commercialisation of CDP870, Celltech's anti-TNF-alpha
           PEGylated antibody fragment, for all indications outside
           of Crohn's disease in North America and major European
           markets.

  6.       Financial Effects of the Transaction

           UCB will finance the acquisition through bank loans. It
           is expected that the transaction will be earnings
           accretive, post synergies and before goodwill and other
           intangibles amortisation, after the second full year.

  7.       Information on Celltech

           Celltech is one of the largest European-based
           biopharmaceutical companies, possessing significant
           discovery and development capabilities, a broad product
           pipeline, and an international pharmaceutical business,
           with operations in the United States and Europe. It
           derives revenues from the licensing of its technologies
           and products and the sale of pharmaceutical products
           through its pharmaceutical business.

           The discovery and development activities are focused on
           treatments for auto-immune and inflammatory disorders
           and oncology. Its pipeline includes candidates
           comprising new chemical entities and antibody-based
           therapeutics, in pre-clinical or clinical development
           and marketing licence registration. Its technology base
           includes a leading position in antibody engineering and
           extensive medicinal chemistry capabilities. Celltech has
           a range of discovery, development and commercialisation
           collaborations with leading pharmaceutical and
           biotechnology companies including: Abgenix, Amgen,
           AstraZeneca, Biogen Idec, Johnson & Johnson, Merck,
           NeoGenesis, Seattle Genetics and Wyeth.

           Celltech Shares are traded on the London Stock Exchange
           and Celltech ADSs are listed on the New York Stock
           Exchange. Cazenove & Co. Limited act as broker to
           Celltech.

           For the year ended 31 December 2003, in accordance with
           generally accepted accounting principles in the United
           Kingdom, Celltech reported turnover of GBP 353.3 million
           (2002: GBP 329.6 million) with operating profit pre
           exceptional items and goodwill of GBP 49.5 million
           (2002: GBP 49.0 million) and net assets of GBP 505.9
           million (2002: GBP 564.4 million).

  8.       Information on UCB

           UCB is a world-class pharmaceutical and specialty
           chemical company. UCB is headquartered in Brussels
           (Belgium) and employs about 11,500 people, of whom more
           than 6,600 are in the pharmaceutical sector.

           UCB operates in two industrial sectors: Pharma and
           Surface Specialties. It currently comprises the parent
           company, UCB S.A., together with about 120 subsidiaries
           and associated companies in Europe, the Americas and
           Asia. UCB also operates on a worldwide basis through its
           agents, distributors and licensees.

           The Pharma Sector researches, produces and markets
           prescription medical products, particularly in the
           fields of allergy / asthma and neurology. Over three
           quarters of the UCB Group's expenditure on research and
           development is in the Pharma Sector, where it accounts
           for about 15 per cent. of turnover. UCB is also present
           in biotechnology, through UCB-Bioproducts, making
           available peptides by extraction or synthesis to the
           scientific community.

           Surface Specialties is focused on the manufacture of
           technically innovative products and solutions for
           surface applications. There are two business units:
           Coating Resins & Additives and Films & Adhesives.

           UCB's shares are traded on Euronext. Based on the
           closing middle-market price of Euro 35.10 per UCB Share
           on 17 May 2004 (the last business day prior to the date
           of this announcement), UCB has a market capitalisation
           of approximately Euro 5.1 billion.

           For the year ended 31 December 2003, in accordance with
           generally accepted accounting principles in Belgium, UCB
           reported group turnover of Euro 2,966 million (2002:
           Euro 2,514 million) with group profit before interest,
           tax and exceptional items of Euro 487 million (2002:
           Euro 503 million) and net assets of Euro 1,784 million
           (2002: Euro 1,565 million).

  9.       Management and Employees

           The board of UCB confirms that, following the Offer
           becoming or being declared unconditional in all
           respects, the existing employment rights, including
           pension rights, of all employees of the Celltech Group
           will be fully safeguarded.

  10.      Celltech Share Plans

           The Offer will (subject to compliance with any
           applicable local law) extend to any Celltech Shares
           issued fully paid (or credited as fully paid) or
           unconditionally allotted or issued prior to the date
           when the Offer closes (or such earlier date as UCB may,
           subject to the provisions of the City Code or with the
           consent of the Panel, decide) as a result of the
           exercise of options granted under the Celltech Share
           Plans.

           As soon as practicable after the Offer becomes or is
           declared unconditional in all respects, UCB will make
           appropriate proposals (taking into account any local
           laws) to holders of options granted under the Celltech
           Share Plans.

  11.      Inducement Fee

           Celltech has agreed to pay a sum to UCB of GBP 15.25
           million (being approximately one per cent. of the value
           of the Offer) in the event that (a) the Directors
           withdraw their unanimous recommendation of the Offer or
           recommend an alternative transaction, resulting in any
           person other than UCB (or any person acting in concert
           with UCB as defined in the City Code) acquiring control
           of Celltech (as defined in the City Code) or a
           substantial part of the business of Celltech; or (b)
           before the Offer lapses or is withdrawn without becoming
           or being declared wholly unconditional, any person
           (other than UCB or a person acting in concert (as
           defined in the City Code) with UCB) announces an
           intention to make a competing offer however effected, to
           acquire the entire issued share capital of Celltech
           (other than Celltech Shares owned by such third party or
           persons acting in concert with it) and, at any time, the
           competing offer becomes or is declared wholly
           unconditional.

  12.      Compulsory acquisition, delisting and de-registration

           If UCB receives acceptances under the Offer in respect
           of, and/or otherwise acquires, 90 per cent. or more of
           the Celltech Shares to which the Offer relates and the
           Offer becomes or is declared unconditional in all
           respects, UCB intends to exercise its rights pursuant to
           the provisions of sections 428 to 430F (inclusive) of
           the Act to acquire compulsorily the remaining Celltech
           Shares to which the Offer relates.

           After the Offer becomes or is declared unconditional in
           all respects, UCB intends to procure the making of an
           application by Celltech to the UK Listing Authority for
           the cancellation of the listing of Celltech's Shares on
           the Official List and to the London Stock Exchange for
           the cancellation of the admission to trading of
           Celltech's Shares on its market for listed securities.
           It is anticipated that cancellation of listing and
           trading will take effect no earlier than 20 business
           days after the Offer becomes or is declared
           unconditional in all respects. UCB also intends to
           procure that Celltech applies for delisting of the
           Celltech ADSs from the New York Stock Exchange. Such
           delistings would significantly reduce the liquidity and
           marketability of any Celltech Shares or Celltech ADSs
           not tendered into the Offer. UCB may also request that
           Celltech terminate the existing deposit agreement
           through which the ADS programme is operated.

           It is also proposed that, following the Offer becoming
           or being declared unconditional in all respects and
           after the Celltech Shares are delisted, Celltech will be
           re-registered as a private company under the relevant
           provisions of the Act.

  13.      Disclosure of Interests in Celltech

           Save for the 493,029 Celltech Shares in respect of which
           UCB has received irrevocable undertakings to accept the
           Offer, neither UCB nor any of the directors of UCB nor
           any other UCB subsidiary, nor, so far as UCB is aware,
           any person acting in concert with UCB for the purposes
           of the Offer, owns, controls or holds any Celltech
           Shares or any securities convertible or exchangeable
           into, or rights to subscribe for, purchase or holds any
           options to purchase any Celltech Shares or has entered
           into any derivative referenced to Celltech Shares which
           remains outstanding.

  14.      Overseas Celltech Shareholders

           The availability of the Offer to persons not resident in
           the United Kingdom may be affected by the laws of the
           relevant jurisdiction. Persons who are not resident in
           the United Kingdom should inform themselves about and
           observe any applicable requirements.

           Under the terms of the Offer, holders of Celltech Shares
           and holders of Celltech ADSs who are located in Belgium,
           Canada, Australia, Japan or the United States or who are
           US persons will not be eligible to receive Loan Notes.

           Notwithstanding the foregoing, UCB retains the right to
           permit the Offer to be accepted and any sale of
           securities pursuant to the Offer to be completed if, in
           its sole discretion, it is satisfied that the
           transaction in question can be undertaken in compliance
           with applicable law and regulation.

           Lazard Freres & Co. LLC is acting as the dealer manager
           for the Offer in the United States.

  15.      Collaboration Agreement

           Celltech has announced today that it has entered into an
           agreement with UCB for the worldwide development and
           marketing of CDP870, Celltech's anti-TNF-alpha PEGylated
           antibody fragment.

           Under the terms of the agreement, Celltech grants UCB
           co-exclusive worldwide rights to develop and
           commercialise CDP870. The license is exclusive for
           rheumatoid arthritis and other indications, excluding
           Crohn's disease. UCB will be responsible for the conduct
           of future clinical studies and all commercialisation
           activities with CDP870 other than in Crohn's disease,
           and will pay Celltech a significant royalty on sales in
           these indications. UCB will also make progress-related
           payments to Celltech dependent upon attaining certain
           project related milestones. Celltech retains
           manufacturing rights and will supply all CDP870 material
           for commercialisation, and will discharge all royalties
           due to third parties. Celltech retains exclusive rights
           for the development and commercialisation of CDP870 in
           Crohn's disease in North America, major European
           markets, Australia and New Zealand with UCB having
           development and commercialisation rights in other
           territories.

           The CDP870 license agreement is not conditional upon the
           success of the proposed Offer for Celltech by UCB.

General

The Offer will be made on the terms and subject to the conditions set out herein and in Appendix I, and to be set out in the Offer Document and the accompanying Acceptance Forms. These will be despatched to Celltech Shareholders and holders of Celltech ADSs and for information only, to participants in the Celltech Share Schemes, in due course. The Offer and acceptances thereof will be governed by English law. The Offer will be subject to the applicable requirements of the City Code, the Panel, the London Stock Exchange, the UK Listing Authority and the Exchange Act.

The availability of the Offer to persons not resident in the United Kingdom or the United States may be affected by the laws of the relevant jurisdictions. Such persons should inform themselves of, and observe, any applicable requirements.

Details of the sources and bases of certain information set out in this announcement are included in Appendix II. Certain terms used in this announcement are defined in Appendix III.

The Offer will be made by UCB and (outside the United States) by Lazard on its behalf.

In connection with the Offer, Panmure Gordon, a division of Lazard is acting as broker to UCB.

Celltech confirms that its current issued share capital (including those represented by Celltech ADSs) comprises 278,128,673 ordinary shares of 50 pence each. The International Securities Identification Number for Celltech Shares is GB0001822765. There are 2,919,709 Celltech ADSs in issue, each Celltech ADS representing two Celltech Shares. The International Securities Identification Number for Celltech ADSs is US1511581027.

Lazard is acting for UCB and no one else in connection with the Offer and will not be responsible to anyone other than UCB for providing the protections afforded to clients of Lazard or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

Morgan Stanley is acting for Celltech and no one else in connection with the Offer and will not be responsible to anyone other than Celltech for providing the protections afforded to clients of Morgan Stanley or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

JPMorgan is acting for Celltech and no one else in connection with the Offer and will not be responsible to anyone other than Celltech for providing the protections afforded to clients of JPMorgan or for providing advice in connection with the Offer, the contents of this announcement or any transaction or arrangement referred to herein.

This press announcement does not constitute an offer or invitation to purchase any securities or a solicitation of an offer to buy any securities, pursuant to the Offer or otherwise. The Offer will be made solely by means of an Offer Document and the Acceptance Forms accompanying the Offer Document, which will contain the full terms and conditions of the Offer, including details of how the Offer may be accepted. In the United States, UCB will file a Tender Offer Statement containing the Offer Document and other related documentation with the SEC on Schedule TO and Celltech will file a Solicitation/Recommendation Statement with the SEC on Schedule 14D-9 on the date the Offer Document is mailed to Celltech Shareholders. Free copies of the Schedule TO, the Schedule 14D-9 and the other related documents to be filed by Celltech or UCB in connection with this Offer will be available from the date the Offer Document is mailed to Celltech Shareholders on the SEC's website at http://www.sec.gov. The Offer Document and Acceptance Forms accompanying the Offer Document will be made available to all Celltech Shareholders at no charge to them. Celltech Shareholders are advised to read the Offer Document and the accompanying Acceptance Forms when they are sent to them because they will contain important information. Celltech Shareholders in the United States are also advised to read the Tender Offer Statement and the Solicitation/Recommendation Statement because they will contain important information.

It should be noted that by virtue of the conflicting provisions of the City Code and the Exchange Act, the Panel has agreed that the Acceptance Condition can be structured so that the Offer cannot become or be declared unconditional as to acceptances until such time as all other conditions of the Offer have been satisfied, fulfilled or, to the extent permitted, waived. The Acceptance Condition in paragraph (a) of Appendix I has been amended accordingly.

Unless otherwise determined by UCB and permitted by applicable law and regulation, the Offer (including the Loan Note Alternative) will not be made, directly or indirectly, in or into, or by use of the mails of, or by any other means or instrumentality (including, without limitation, telephonically or electronically) of interstate or foreign commerce of, or of any facility of a national securities exchange of Canada, nor will it be made in or into Belgium, Australia or Japan and the Offer will not be capable of acceptance by any such use, means, instrumentality or facilities or from within Belgium, Australia, Canada or Japan. Accordingly, unless otherwise determined by UCB and permitted by applicable law and regulation, neither copies of this announcement nor any other documents relating to the Offer are being, or may be, mailed or otherwise forwarded, distributed or sent in or into Belgium, Australia, Canada or Japan and persons receiving such documents (including custodians, nominees and trustees) must not distribute or send them in, into or from such jurisdictions.

The Loan Notes to be issued pursuant to the Loan Note Alternative have not been, and will not be, listed on any stock exchange and have not been and will not be registered under the Securities Act or under any relevant securities laws of any state or other jurisdiction of the United States, or under the relevant securities laws of Belgium, Australia, Canada or Japan or any other jurisdiction. Accordingly, unless an exemption under such relevant laws is available, Loan Notes may not be offered, sold, re-sold or delivered, directly or indirectly, in, into or from the United States, Belgium, Australia, Canada or Japan or any other jurisdiction in which an offer of Loan Notes would constitute a violation of relevant laws or require registration of the Loan Notes, or to or for the account or benefit of any US person or resident of Belgium, Australia, Canada or Japan or any other such jurisdiction.

The Panel wishes to draw the attention of member firms of the New York Stock Exchange to certain UK dealing disclosure requirements during the offer period. The offer period (in accordance with the City Code, which is published and administered by the Panel) commences at the time when an announcement is made of a proposed or possible offer, with or without terms. Celltech has equity securities traded on the London Stock Exchange and the New York Stock Exchange.

The above disclosure requirements are set out in more detail in Rule 8 of the City Code. In particular, Rule 8 requires public disclosure of dealings during the offer period by persons who own or control, or who would as a result of any transaction own or control, one per cent. or more of any class of relevant securities of the offeree company. Relevant securities include Celltech Shares, Celltech ADSs, instruments convertible into Celltech Shares or Celltech ADSs and options in respect of any of the foregoing and derivatives referenced to any of the foregoing. This requirement will apply until the first closing date or, if this is later, the date when the Offer becomes or is declared unconditional or lapses.

Disclosure should be made on an appropriate form by no later than 12:00 noon (London time), 7:00 a.m. (New York City time), on the business day following the date of the dealing transaction. These disclosures should be sent to a Regulatory Information Service and a copy faxed to the Panel (+44 (0) 20 7638 1554).

The Panel requests that member firms advise those of their clients who wish to deal in the relevant securities of Celltech, whether in the United States or in the United Kingdom, that they may be affected by these requirements. If there is any doubt as to their application the Panel should be consulted (telephone number: +44 (0) 20 7382 9026, fax number: +44 (0) 20 7638 1554).

The directors of UCB accept responsibility for the information contained in this announcement, other than that relating to the Celltech Group, the directors of Celltech and their immediate families, related trusts and persons connected with them, for which the directors of Celltech accept responsibility as set out below. To the best of the knowledge and belief of the directors of UCB (who have taken all reasonable care to ensure that such is the case), the information contained in this announcement for which they are responsible is in accordance with the facts and does not omit anything to affect the import of such information.

The directors of Celltech accept responsibility for the information contained in this announcement relating to the Celltech Group, themselves and their immediate families, related trusts and persons connected with them. To the best of the knowledge and belief of the directors of Celltech (who have taken all reasonable care to ensure that such is the case), the information contained in this announcement for which they are responsible is in accordance with the facts and does not omit anything likely to affect the import of such information.

This press announcement includes "forward-looking statements" relating to the Offer, UCB and Celltech that are subject to known and unknown risks and uncertainties many of which are outside of UCB's and Celltech's control and are difficult to predict, that may cause actual results to differ materially from any future results expressed or implied from such forward-looking statements. Important factors that could cause actual results to differ materially from such expectations include, without limitation: the inability to obtain necessary regulatory approvals in the context of the Offer or to obtain them on acceptable terms; the inability to integrate successfully Celltech within UCB or to realise synergies from such integration following the acquisition; costs related to the acquisition of Celltech; the economic environment of the industries in which UCB and Celltech operate; costs associated with research and development; changes in the prospects for products in the research and development pipeline of UCB or Celltech; dependence on the existing management of UCB and Celltech; changes or uncertainties in UK or US federal or state tax laws or the administration of such laws; changes or uncertainties in the laws or regulations applicable to the markets in which UCB and Celltech operate, including those of the Federal Drug Administration in the United States; and other factors detailed in Celltech's filings with the SEC.



                        APPENDIX I

      CONDITIONS AND CERTAIN FURTHER TERMS OF THE OFFER


 The Offer will be subject to the following conditions:




  (a)    valid acceptances of the Offer being received (and not,
         where permitted, withdrawn) by 3.00 p.m. (London time),
         10.00 a.m. (New York City time) on the twentieth US
         business day following the posting of the Offer Document
         or such later time(s) and/or date(s) as UCB may, subject
         to the rules of the City Code and in accordance with the
         Exchange Act, decide in respect of not less than 90 per
         cent. in nominal value (or such lesser percentage as UCB
         may decide) of the Celltech Shares (including Celltech
         Shares represented by Celltech ADSs) to which the Offer
         relates, provided that this condition will not be
         satisfied unless UCB and/or any of its wholly-owned
         subsidiaries shall have acquired, or agreed to acquire,
         pursuant to the Offer or otherwise, Celltech Shares
         (including Celltech Shares represented by Celltech ADSs)
         carrying, in aggregate more than 50 per cent. of the
         voting rights normally exercisable at a general meeting of
         Celltech, including for this purpose (to the extent, if
         any, required by the Panel) any such voting rights
         attaching to any Celltech Shares (including Celltech
         Shares represented by Celltech ADSs) that are
         unconditionally allotted or issued before the Offer
         becomes or is declared unconditional as to acceptances
         whether pursuant to the exercise of any outstanding
         subscription or conversion rights or otherwise, and for
         the purposes of this condition:




      (i)      Celltech Shares (including Celltech Shares
               represented by Celltech ADSs) which have been
               unconditionally allotted but not issued shall be
               deemed to carry the voting rights they will carry on
               issue;

      (ii)     the expression "Celltech Shares (including Celltech
               Shares represented by Celltech ADSs) to which the
               Offer relates" shall be construed in accordance with
               sections 428 to 430F of the Companies Act; and

      (iii)    valid acceptances also shall be treated as having
               been received in respect of any Celltech Shares
               (including Celltech Shares represented by Celltech
               ADSs) which UCB shall, pursuant to section 429(8) of
               the Companies Act, be treated as having acquired or
               contracted to acquire by virtue of acceptance of the
               Offer;




      provided further that unless UCB otherwise determines, this
      condition (a) shall be capable of being satisfied only at a
      time when all of the other conditions (b) to (m) inclusive
      have been either satisfied, fulfilled or, to the extent
      permitted, waived;




             (b)    subject to condition (e) below:




      (i)      the UK Office of Fair Trading ("OFT") indicating in
               terms reasonably satisfactory to UCB that it does
               not believe that the proposed acquisition of
               Celltech by UCB (the "Transaction") creates a
               relevant merger situation within the meaning of
               section 23 of the Enterprise Act 2002 ("EA"); or

      (ii)     the OFT indicating in terms reasonably satisfactory
               to UCB that it has decided not to refer the
               Transaction or any part of it to the Competition
               Commission ("CC"); or

      (iii)    the period for considering any merger notice given
               to the OFT under section 96 of the EA by UCB having
               expired without any such reference being made,
               provided that sections 100(1)(a), (d) and (f) of the
               EA do not apply in relation to such merger;




  (c)    subject to condition (e) below, UCB obtaining an approval,
         or being deemed to have obtained an approval, from the
         German competition authority, the Federal Cartel Office
         ("Bundeskartellamt"), in terms reasonably satisfactory to
         UCB, in relation to the Transaction;

  (d)    subject to condition (e) below, if the Transaction
         requires notification to the Austrian Cartel Court under
         the Austrian Cartel Act ("Cartel Act"), then:




      (i)      the Austrian Cartel Court issuing a clearance
               certificate pursuant to Section 42b (1) Cartel Act,
               in terms reasonably satisfactory to UCB; or

      (ii)     the four week period under Section 42b (1) Cartel
               Act expiring without an in-depth investigation
               having been opened or requested; or

      (iii)    the Austrian Cartel Court not prohibiting the
               Transaction within a period of five months from the
               receipt of the complete notification; or

      (iv)     the Austrian Cartel Court issuing a final order
               pursuant to Section 42b (2) no 1 Cartel Act which
               sets forth that the Transaction does not constitute
               a concentration within the meaning of Section 41
               Cartel Act; or

      (v)      the Austrian Cartel Court issuing a final order
               pursuant to Section 42b (2) no 3 Cartel Act which
               sets forth, in terms reasonably satisfactory to UCB,
               that the concentration will not be prohibited;




  (e)    if a request to the European Commission is made by the
         competent authorities of one or more Member States under
         Article 22 of Council Regulation (EC) No 139/2004 (the
         "Regulation") in relation to the Transaction or any part
         of it and is accepted by the European Commission:




      (i)      the European Commission issuing a decision pursuant
               to Article 6(1)(b) of the Regulation in terms
               reasonably satisfactory to UCB declaring that the
               Transaction or, if applicable, the relevant part of
               the Transaction, is compatible with the common
               market; and

      (ii)     to the extent that the OFT retains jurisdiction over
               any part of the Transaction, one of the conditions
               set out in conditions (b)(i) to (iii) above being
               satisfied in relation to each such part of the
               Transaction; and

      (iii)    to the extent that the Bundeskartellamt retains
               jurisdiction over any part of the Transaction, the
               condition set out in condition (c) above being
               satisfied in relation to each such part of the
               Transaction; and

      (iv)     to the extent that the Austrian Cartel Court retains
               jurisdiction over any part of the Transaction, one
               of the conditions set out in conditions (d)(i) to
               (v) above being satisfied in relation to each such
               part of the Transaction;




  (f)    all required filings having been made under the United
         States Hart-Scott-Rodino Antitrust Improvements Act of
         1976 (as amended) and the rules and regulations thereunder
         and all applicable waiting periods with respect thereto
         having expired or been terminated as appropriate, in each
         case in connection with the Transaction;

  (g)    all necessary notifications and filings required by law or
         regulation having been made, all or any applicable waiting
         and other time periods (including any extensions thereof
         (including requests for additional information)) under any
         applicable legislation or regulation of any jurisdiction
         having expired, lapsed or terminated and any approvals or
         clearances required by law or regulation having been
         obtained to the reasonable satisfaction of UCB as
         appropriate, in each case, in respect of the Offer, its
         implementation and the acquisition of any shares in, or
         control of, Celltech (or any member of the Celltech Group)
         by UCB or any member of the UCB Group and all necessary
         statutory and regulatory obligations in connection with
         the Offer in any jurisdiction having been complied with;

  (h)    other than investigations and waiting periods listed in
         condition (g), no central bank, government or
         governmental, quasi-governmental, supranational, statutory
         or regulatory body or association, institution or agency
         (including any trade agency) or any court or other body
         (including any professional or environmental body) or
         person in any jurisdiction (each a "Relevant Authority")
         having decided to take, instituted or threatened any
         action, proceeding, suit, investigation, enquiry or
         reference or enacted, made or proposed and there not
         continuing to be outstanding any statute, regulation,
         order or decision that would or might reasonably be
         expected to:




      (i)       make the Offer, its implementation or the
                acquisition or the proposed acquisition of any
                Celltech Shares (including Celltech Shares
                represented by Celltech ADSs) in, or control of,
                Celltech by any member of the UCB Group void,
                unenforceable or illegal or directly or indirectly
                prohibit or restrict, delay or interfere with the
                implementation of, or impose material additional
                conditions or obligations with respect to, or
                otherwise challenge, the Offer, its implementation
                or the acquisition of any shares in, or control of,
                Celltech by any member of the UCB Group;

      (ii)      result in a delay in the ability of UCB or any
                member of the UCB Group, or render UCB or any
                member of the UCB Group unable, to acquire all of
                the Celltech Shares (including Celltech Shares
                represented by Celltech ADSs) or require a
                divestiture by UCB or any member of the UCB Group
                of any Celltech Shares (including Celltech Shares
                represented by Celltech ADSs);

      (iii)     require, prevent or materially delay the
                divestiture (or alter the terms of any proposed
                divestiture) by any member of the Wider UCB Group
                or any member of the Wider Celltech Group of all or
                any part of their respective businesses, assets or
                properties or impose any limitation on their
                ability to conduct all or any part of their
                respective businesses and to own any of their
                respective assets or properties to an extent which
                is material in the context of the Wider Celltech
                Group taken as a whole or the UCB Group taken as a
                whole (as the case may be);

      (iv)      impose any material limitation on, or result in any
                material delay in, the ability of any member of the
                UCB Group to acquire or hold Celltech Shares
                (including Celltech Shares represented by Celltech
                ADSs) or other securities (or the equivalent) in
                any member of the Celltech Group or to exercise
                effectively, directly or indirectly, all or any
                rights of ownership of Celltech Shares (including
                Celltech Shares represented by Celltech ADSs) or
                other securities (or the equivalent) in, or to
                exercise management control over, any member of the
                Celltech Group or on the ability of any member of
                the Celltech Group to hold or exercise effectively,
                directly or indirectly, all or any rights of
                ownership of shares or other securities (or the
                equivalent) in, or to exercise management control
                over, any other member of the Celltech Group;

      (v)       result in any member of the Celltech Group ceasing
                to be able to carry on business under any name
                which it presently does so to an extent which is
                material in the context of the Wider Celltech Group
                taken as a whole or the UCB Group taken as a whole
                (as the case may be);

      (vi)      require any member of the UCB Group or of the
                Celltech Group to acquire or offer to acquire any
                shares or other securities (or the equivalent) in
                any member of the Celltech Group or any member of
                the Wider UCB Group owned by any third party (other
                than in the implementation of the Offer) to an
                extent which is material in the context of the
                Wider Celltech Group taken as a whole or the UCB
                Group taken as a whole (as the case may be);

      (vii)     impose any limitation on the ability of any member
                of the Wider UCB Group or the Celltech Group to
                integrate or co-ordinate its business, or any part
                of it, with the businesses or any part of the
                businesses of any other member of the Wider UCB
                Group and/or the Celltech Group to an extent which
                is material in the context of the Wider Celltech
                Group taken as a whole or the UCB Group taken as a
                whole (as the case may be); or

      (viii)    otherwise adversely affect the business, assets,
                financial or trading position or profits or
                prospects of any member of the Wider UCB Group or
                of the Wider Celltech Group in a manner which is
                adverse to and material in the context of the UCB
                Group taken as a whole or the Wider Celltech Group
                taken as a whole (as the case may be),

                and all applicable waiting and other time periods
                during which any such Relevant Authority could
                decide to take, institute, implement or threaten
                any such action, proceeding, suit, investigation,
                enquiry or reference having expired, lapsed or been
                terminated;




  (i)    all notifications and filings have been made in connection
         with the Offer and all authorisations, orders, grants,
         recognitions, confirmations, licences, consents,
         clearances, certificates, permissions and approvals
         ("Authorisations") necessary or appropriate in any
         jurisdiction for, in respect of or resulting from the
         Offer, its implementation or the proposed acquisition by
         UCB or any member of the UCB Group of any shares in
         Celltech or control of Celltech (or any member of the
         Celltech Group) being obtained in terms and in a form
         reasonably satisfactory to UCB from appropriate Relevant
         Authorities or from any persons or bodies with whom any
         member of the Wider UCB Group or the Celltech Group has
         entered into contractual arrangements and such
         authorisations, together with all authorisations necessary
         or appropriate for any member of the Celltech Group to
         carry on its business where such business is material in
         the context of the Wider Celltech Group as a whole
         remaining in full force and effect and no intimation of
         any intention to revoke, suspend, restrict or modify or
         not to renew any such authorisations having been made;

  (j)    save as fairly disclosed in the annual report and accounts
         of the Celltech Group for the year ended 31 December 2003,
         or by or on behalf of Celltech to UCB, or as publicly
         announced to a Regulatory Information Service by or on
         behalf of Celltech, (in each such case) prior to 18 May
         2004, there being no provision of any agreement,
         arrangement, lease, licence, permit or other instrument to
         which any member of the Wider Celltech Group is a party or
         by or to which any such member or any of its assets is or
         may be bound, entitled or subject which, as a result of
         the making of the Offer, its implementation or the
         acquisition or proposed acquisition by UCB of any shares
         in, or change in the control or management of, Celltech or
         otherwise, would or might reasonably be expected to result
         in, and no event having occurred which, under any
         provision of any agreement, arrangement, licence, permit
         or other instrument to which any member of the Wider
         Celltech Group is a party or by or to which any such
         member or any of its assets may be bound, entitled or
         subject, could reasonably be expected to result in, to an
         extent which is, in any case, material in the context of
         the Wider Celltech Group taken as a whole:




      (i)       any monies borrowed by or any other indebtedness
                (actual or contingent) of any such member being or
                becoming repayable or being capable of being
                declared repayable immediately or earlier than the
                stated repayment date or the ability of such member
                to borrow monies or incur any indebtedness being
                withdrawn or inhibited or any such arrangement,
                agreement, licence or instrument relating to any
                monies borrowed or indebtedness being terminated or
                modified or any onerous obligations arising or any
                action being taken or arising thereunder;

      (ii)      the creation or enforcement of any mortgage, charge
                or other security interest over the whole or any
                part of the business, property or assets of any
                such member or any such security interest (whenever
                arising or having arisen) becoming enforceable;

      (iii)     any assets or interests of any such member being or
                falling to be disposed of or charged or any right
                arising under which any such asset or interest
                could be required to be disposed of or charged
                other than in the ordinary course of business;

      (iv)      the interest or business of any such member in or
                with any other person, firm or company (or any
                agreements or arrangements relating to such
                interest or business) being terminated or adversely
                modified or affected;

      (v)       any such member ceasing to be able to carry on
                business under any name under which it presently
                does so;

      (vi)      the value of any such member or its financial or
                trading position or profits or prospects being
                prejudiced or adversely affected;

      (vii)     any such agreement, arrangement, licence or other
                instrument being terminated or adversely modified
                or any onerous obligation arising or any adverse
                action being taken or arising thereunder; or

      (viii)    the creation of any liabilities (actual or
                contingent) by any such member;




  (k)    since 31 December 2003 (except as publicly announced to a
         Regulatory Information Service by or on behalf of Celltech
         before 18 May 2004 or as fairly disclosed in the annual
         report and accounts of the Celltech Group for the year
         ended 31 December 2003, or by or on behalf of Celltech to
         UCB prior to 18 May 2004), no member of the Celltech Group
         having:




      (i)       save as between Celltech and its wholly-owned
                subsidiaries prior to 18 May 2004 or upon the
                exercise of rights to subscribe for Celltech Shares
                pursuant to options granted under the Celltech
                Share Option Schemes prior to such date, issued or
                agreed to issue or authorised the issue of
                additional shares of any class, or securities
                convertible into or exchangeable for, or rights,
                warrants or options to subscribe for or acquire,
                any such shares or convertible securities;

      (ii)      recommended, declared, paid or made or proposed to
                recommend, declare, pay or make any bonus issue,
                dividend or other distribution, whether payable in
                cash or otherwise, other than a distribution by any
                wholly-owned subsidiary of Celltech to Celltech or
                any of its wholly owned subsidiaries;

      (iii)     save for transactions between Celltech and its
                wholly-owned subsidiaries, implemented or
                authorised any merger or demerger or acquired or
                disposed of or, other than in the ordinary course
                of business, transferred, mortgaged or charged, or
                created any other security interest over, any
                material asset or any right, title or interest in
                any material asset;

      (iv)      implemented or authorised any reconstruction,
                amalgamation or scheme of arrangement;

      (v)       other than between Celltech and its wholly-owned
                subsidiaries or between such wholly-owned
                subsidiaries, purchased, redeemed or repaid any of
                its own shares or other securities or reduced or
                made or authorised any other change in its share
                capital;

      (vi)      other than between Celltech and its wholly-owned
                subsidiaries or between such wholly-owned
                subsidiaries, made or authorised any change in its
                loan capital or issued or authorised the issue of
                any debentures or incurred or increased any
                indebtedness or contingent liability;

      (vii)     entered into, varied or terminated, or authorised
                the entry into, variation or termination of, any
                contract, commitment, agreement, proposal or
                arrangement (whether in respect of capital
                expenditure or otherwise) which is outside the
                ordinary course of trading or which is of a
                long-term, onerous or unusual nature or magnitude
                or which involves or could involve an obligation of
                a nature or magnitude which is material in the
                context of the Wider Celltech Group (taken as a
                whole) or which is or is likely to be restrictive
                on the business of any member of the Wider Celltech
                Group or the Wider UCB Group to an extent which is
                material in the context of the Wider Celltech Group
                or the UCB Group (as appropriate) taken as a whole;

      (viii)    been unable, or admitted in writing that it is
                unable, to pay its debts or having stopped or
                suspended (or threatened to stop or suspend)
                payment of its debts generally or ceased or
                threatened to cease carrying on all or a
                substantial part of its business;

      (ix)      taken any corporate action or had any legal
                proceedings started or threatened against it for
                its winding-up (voluntary or otherwise),
                dissolution or reorganisation (or for any analogous
                proceedings or steps in any jurisdiction) or for
                the appointment of a receiver, administrator,
                administrative receiver, trustee or similar officer
                (or for the appointment of any analogous person in
                any jurisdiction) of all or any of its assets and
                revenues or appointed any analogous person in any
                jurisdiction;

      (x)       waived, compromised or settled any claim which is
                material;

      (xi)      entered into or varied the terms of any service
                agreement or arrangement with any director or
                senior executive of Celltech;

      (xii)     made or consented to any significant change to the
                terms of the trust deeds constituting the pension
                schemes established for its directors and/or
                employees and/or their dependants or to the
                benefits which accrue, or to the pensions which are
                payable thereunder, or to the basis on which
                qualification for or accrual or entitlement to such
                benefits or pensions are calculated or determined,
                or to the basis upon which the liabilities
                (including pensions) of such pension schemes are
                funded or made, or agreed or consented to any
                change to the trustees; or

      (xiii)    entered into any contract, commitment or
                arrangement or passed any resolution or made any
                offer (which remains open for acceptance) with
                respect to, or proposed or announced any intention
                to effect or propose, any of the transactions,
                matters or events referred to in sub-paragraphs (i)
                to (xii) of this condition (k);




  (l)    since 31 December 2003 (except as publicly announced to a
         Regulatory Information Service by or on behalf of Celltech
         before 18 May 2004 or as fairly disclosed in the annual
         report and accounts of the Celltech Group for the year
         ended 31 December 2003, or by or on behalf of Celltech to
         UCB prior to 18 May 2004):




      (i)      no adverse change having occurred in the business,
               assets, financial or trading position or profits or
               prospects of any member of the Wider Celltech Group
               to an extent which is material to the Wider Celltech
               Group taken as a whole;

      (ii)     no litigation, arbitration proceedings, prosecution
               or other legal proceedings having been threatened,
               announced, instituted or remaining outstanding by,
               against or in respect of any member of the Wider
               Celltech Group or to which any member of the Wider
               Celltech Group is a party (whether as claimant or
               defendant or otherwise) and no investigation by any
               Relevant Authority or other investigative body
               against or in respect of any member of the Celltech
               Group having been threatened, announced, instituted
               or remaining outstanding by, against or in respect
               of any member of the Wider Celltech Group which, in
               any such case, might be reasonably likely to
               adversely affect any member of the Wider Celltech
               Group to an extent which is material to the Wider
               Celltech Group (taken as a whole); and

      (iii)    no contingent or other liability having arisen which
               would or might be reasonably likely to adversely
               affect any member of the Wider Celltech Group to an
               extent which is material to the Wider Celltech Group
               taken as a whole;




  (m)    except as fairly disclosed to UCB in the annual report and
         accounts of the Celltech Group for the year ended 31
         December 2003, or by or on behalf of Celltech prior to 18
         May 2004, UCB not having discovered that:




      (i)      any financial, business or other information
               concerning the Wider Celltech Group disclosed at any
               time by or on behalf of any member of the Wider
               Celltech Group is misleading, contains a
               misrepresentation of fact or omits to state a fact
               necessary to make the information contained therein
               not misleading and which is material in the context
               of the Wider Celltech Group (taken as a whole);

      (ii)     any member of the Wider Celltech Group is subject to
               any liability, contingent or otherwise, which should
               have been but is not disclosed in the annual report
               and accounts of Celltech for the year ended 31
               December 2003 and which is material in the context
               of the Wider Celltech Group (taken as a whole);

      (iii)    any past or present member of the Wider Celltech
               Group has failed to comply in any material respect
               with any applicable legislation or regulations of
               any jurisdiction or any notice or requirement of any
               Relevant Authority with regard to the storage,
               disposal, discharge, spillage, release, leak or
               emission of any waste or hazardous or harmful
               substance or any substance likely to impair the
               environment or harm human or animal health or
               otherwise relating to environmental matters or that
               there has been any such storage, presence, disposal,
               discharge, spillage, release, leak or emission
               (whether or not the same constituted non-compliance
               by any person with any such legislation or
               regulation, and whenever the same may have taken
               place), any of which non-compliance would be likely
               to give rise to any material liability (whether
               actual or contingent) or cost on the part of any
               member of the Wider Celltech Group and which is
               material in the context of the Wider Celltech Group
               (taken as a whole); or

      (iv)     there is, or is reasonably likely to be, any
               material obligation or liability (whether actual or
               contingent) to make good, repair, re-instate or
               clean up any property now or previously owned,
               occupied, operated or made use of or controlled by
               any past or present member of the Celltech Group
               under any environmental legislation, regulation,
               notice, circular or order of any Relevant Authority
               in any jurisdiction, in each case to an extent which
               is material in the context of the Wider Celltech
               Group (taken as a whole).

If UCB is required by the Panel to make an offer for Celltech Shares under the provisions of Rule 9 of the City Code, then UCB may make such alterations to any of the above conditions as are necessary to comply with the provisions of that Rule.

UCB reserves the right to waive all or any of conditions (b) to (m) above inclusive, in whole or in part. The Offer will lapse unless all the above conditions are fulfilled or (if capable of waiver) waived or, where appropriate, determined by UCB to have been or remain satisfied by 3.00 p.m. (London time), 10.00 a.m. (New York City time) on the twentieth US business day following the posting of the Offer Document (or such later date as UCB may determine, in accordance with the City Code and the Exchange Act). UCB shall be under no obligation to waive or treat as fulfilled any of conditions (b) to (m) inclusive by a date earlier than the latest date for the fulfilment thereof notwithstanding that the other conditions of the Offer may at such earlier date have been waived or fulfilled and that there are at such earlier date no circumstances indicating that any of such conditions may not be capable of fulfilment.

If before 3.00 p.m. (London time), 10.00 a.m. (New York City time) on the twentieth US business day following the posting of the Offer Document or the date when the Offer becomes unconditional as to acceptances (whichever is the later):



  (i)         the OFT has referred the Offer to the Competition
              Commission; or

  (ii)        the European Commission has initiated proceedings in
              respect of the Offer under Article 6(1)(c) of the
              Regulation,

the Offer will lapse.

For the purposes of this Appendix:

"Wider Celltech Group" means Celltech and its subsidiary undertakings, associated undertakings and any other undertakings in which Celltech and such undertakings (aggregating their interests) have a substantial interest; and

"Wider UCB Group" means UCB and its subsidiary undertakings, associated undertakings and any other undertakings in which UCB and such undertakings (aggregating their interests) have a substantial interest.

For these purposes "subsidiary undertaking", "associated undertaking" and "undertaking" have the meanings given by the Companies Act 1985 (but for these purposes ignoring paragraph 20(1)(b) of Schedule 4A to the Companies Act 1985) and "substantial interest" means a direct or indirect interest in 20 per cent. of more of the equity capital of an undertaking.



                            APPENDIX II

         SOURCES OF INFORMATION AND BASES OF CALCULATION




  (a)    The value placed by the Offer on the existing share
         capital of Celltech is based on 278,128,673 Celltech
         Shares in issue on 17 May 2004.

  (b)    The closing middle-market prices of Celltech Shares are
         derived from the London Stock Exchange Daily Official List
         for the relevant dates.

  (c)    Unless otherwise stated, the financial information
         relating to Celltech is extracted from the audited
         financial statements of Celltech for the financial year
         ended 31 December 2003.

  (d)    The value as stated in the announcement placed on the
         existing share capital of UCB is based on 145,933,000 UCB
         shares in issue on 17 May 2004.

  (e)    The closing middle-market prices of UCB shares are derived
         from the Euronext La Cote Officielle for the relevant
         dates.

  (f)    Unless otherwise stated, the financial information
         relating to UCB is extracted from the audited financial
         statements of UCB for the financial year ended 31 December
         2003.

         Exchange rates

         Exchange rates of GBP 1 : USD 1.7675 and GBP 1 : Euro
         1.4721 as per Bloomberg at 4.30 p.m. London time 17th May
         2004 have been used throughout this announcement.

                          APPENDIX III

                          DEFINITIONS

 The following definitions apply throughout this announcement unless
 the context otherwise requires:




  "Acceptance Condition"            the condition as set out in
                                    paragraph (a) of Appendix I to
                                    this announcement

  "Acceptance Forms"                the Form of Acceptance and, in
                                    relation to holders of Celltech
                                    ADSs only, the Letter of
                                    Transmittal and the Notice of
                                    Guaranteed Delivery, relating
                                    to the Offer

  "Act" or "Companies Act"          the Companies Act 1985, as
                                    amended

  "business day"                    any day, other than a Saturday
                                    or Sunday or a public holiday
                                    in the UK, consisting of the
                                    time period from 12:01 a.m.
                                    until and including 12:00
                                    midnight (London time)

  "Celltech" or the "Company"       Celltech Group plc

  "Celltech Group" or the "Group"   Celltech and its subsidiary
                                    undertakings and, where the
                                    context permits, each of them

  "Celltech ADRs"                   American Depositary Receipts
                                    issued by Celltech under the
                                    deposit agreement representing
                                    the right to Celltech ADSs

  "Celltech ADSs"                   American Depositary Shares,
                                    each representing two Celltech
                                    Shares, evidenced by Celltech
                                    ADRs

  "Celltech Shareholders"           holders of Celltech Shares from
                                    time to time

  "Celltech Share Plans"            The Celltech Group plc
                                    Sharesave Scheme, the
                                    Chiroscience Group Sharesave
                                    Scheme, the Celltech Group 1993
                                    Savings Related Share Option
                                    Scheme, the Celltech Group 1993
                                    Executive Share Option Scheme,
                                    the Chiroscience 1997 All
                                    Employee Share Option Scheme,
                                    the Chiroscience Group (No. 1)
                                    Executive Share Option Scheme,
                                    the Chiroscience Group (No. 2)
                                    Executive Share Option Scheme,
                                    the Darwin Molecular
                                    Technologies, Inc. 1993 Stock
                                    Option Plan, the Medeva Plc
                                    1996 Executive Share Option
                                    Scheme, the Medeva Plc
                                    Executive Share Option Scheme,
                                    the Medeva Plc United States
                                    Executive Stock Option Plan,
                                    the Celltech Chiroscience
                                    Executive Share Option Scheme
                                    1999, the Celltech Group plc
                                    2001 Discretionary Share Option
                                    Scheme and the Celltech
                                    Deferred Bonus Plan

  "Celltech Share(s)"               the existing unconditionally
                                    allotted or issued and fully
                                    paid ordinary shares of 50
                                    pence each in the capital of
                                    Celltech (including those
                                    represented by Celltech ADSs)
                                    and any further such shares
                                    which are unconditionally
                                    allotted or issued prior to the
                                    time at which the Offer ceases
                                    to be open for acceptance (or,
                                    subject to the provisions of
                                    the City Code, such earlier
                                    time and/or date as UCB may
                                    decide)

  "City Code"                       The City Code on Takeovers and
                                    Mergers

  "Directors" or "Celltech Board"   the directors of Celltech

  "Euro"                            euros, the lawful currency of
                                    the Euro-zone

  "Exchange Act"                    the United States Securities
                                    Exchange Act of 1934 (as
                                    amended) and the rules and
                                    regulations promulgated
                                    thereunder

  "Form of Acceptance"              the form of acceptance,
                                    authority and election for use
                                    by Celltech Shareholders in
                                    connection with the Offer

  "FSA"                             Financial Services Authority

  "JPMorgan"                        J.P. Morgan plc

  "Lazard"                          Lazard & Co., Limited

  "Letter of Transmittal"           in relation to Celltech ADSs,
                                    the letter of transmittal
                                    relating to the Offer which is
                                    being sent with the Offer
                                    Document for use by holders of
                                    Celltech ADSs wishing to accept
                                    the Offer

  "LIBOR"                           the interest rate offered in
                                    the market for London
                                    inter-bank six month sterling
                                    deposits on the first business
                                    day of the relevant interest
                                    period which appears on the
                                    Telerate page 3750 at or about
                                    11:00 a.m. on the same date

  "Loan Note Alternative"           the alternative under the Offer
                                    whereby Celltech Shareholders
                                    (other than certain Overseas
                                    Shareholders) who validly
                                    accept the Offer may elect to
                                    receive Loan Notes instead of
                                    all or part of the cash
                                    consideration to which they
                                    would otherwise have been
                                    entitled under the Offer

  "Loan Notes"                      the loan notes of UCB to be
                                    issued pursuant to the Loan
                                    Note Alternative

  "London Stock Exchange"           London Stock Exchange plc

  "Morgan Stanley"                  Morgan Stanley & Co. Limited

  "Morgan Stanley Group"            Morgan Stanley Dean Witter &
                                    Co. and its affiliates

  "New York Stock Exchange" or      New York Stock Exchange, Inc.
  "NYSE"

  "Notice of Guaranteed Delivery"   the notice of guaranteed
                                    delivery relating to the Offer
                                    for use by holders of Celltech
                                    ADSs, which will accompany the
                                    Offer Document

  "Offer"                           the recommended cash offer to
                                    be made by UCB and outside the
                                    United States by Lazard on its
                                    behalf to acquire the whole of
                                    the issued and to be issued
                                    share capital of Celltech, on
                                    the terms and subject to the
                                    conditions to be set out in the
                                    Offer Document and the
                                    Acceptance Forms including,
                                    where the context so requires,
                                    any subsequent revision,
                                    variation, extension or renewal
                                    of such offer

  "Offer Document"                  the document containing and
                                    setting out the terms and
                                    conditions of the Offer to be
                                    sent to Celltech Shareholders

  "Official List"                   the Official List of the UK
                                    Listing Authority

  "Overseas Celltech                Celltech Shareholders who are
  Shareholders"                     resident in or nationals or
                                    citizens of jurisdictions
                                    outside the United Kingdom or
                                    United States or who are
                                    nominees of, or custodians or
                                    trustees for, citizens or
                                    nationals of other countries

  "Panel"                           the Panel on Takeovers and
                                    Mergers

  "SEC"                             the United States Securities
                                    and Exchange Commission

  "Securities Act"                  the United States Securities
                                    Act of 1933 (as amended) and
                                    the rules and regulations
                                    promulgated thereunder

  "Sterling" or "GBP"               pounds sterling, the lawful
                                    currency of the United Kingdom

  "UCB"                             UCB S.A.

  "UCB Group"                       UCB and its subsidiary
                                    undertakings and, where the
                                    context admits, each of them

  "UCB Shares"                      the shares of UCB S.A.

  "UK" or "United Kingdom"          United Kingdom of Great Britain
                                    and Northern Ireland

  "UK Listing Authority"            the FSA acting in its capacity
                                    as the competent authority for
                                    listing under Part VI of the
                                    Financial Services and Markets
                                    Act 2000

  "United States" or "US"           the United States of America,
                                    its territories and
                                    possessions, any State of the
                                    United States of America and
                                    the District of Columbia

  "US business days"                any day, other than Saturday,
                                    Sunday or a federal holiday in
                                    the United States and
                                    consisting of the time period
                                    from 12:01 am to 12:00 midnight
                                    Eastern (US) time

  "US dollar" or "USD"              the lawful currency of the
                                    United States

  "US Person"                       a US person as defined in
                                    Regulation S under the
                                    Securities Act

All times referred to are London time unless otherwise stated.



                  This information is provided by RNS
       The company news service from the London Stock Exchange
PRESS ENQUIRIES:

UCB                                 Tel: +32 (2) 559 92 99
Roch Doliveux
Laurence Battaille

Lazard (Financial adviser to UCB)

London                              Tel: +44 (0)20 7187 2000
William Rucker
David Gluckman
Will Thompson

New York                                Tel: +1 (212) 632 6000
Stephen Sands
Jason Bernhard

Paris                                   Tel: +33 (1) 44 13 01 11
Matthieu Bucaille
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Laurent Perpere                   Tel: +33 (6) 21 06 40 33
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Celltech                           Tel: +44 (0)1753 534 655
Goran Ando
Peter Allen
Richard Bungay

Morgan Stanley (Joint financial           Tel: +44 (0)20 7425 5000
adviser to Celltech)
Simon Robey
Mark Warham

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Celltech)
Bernard Taylor
Julian Oakley

Brunswick Group (Media adviser to       Tel: +44 (0)20 7404 5959
Celltech)
Jon Coles
Wendel Carson