With reference to the UK referendum Nasdaq Derivatives Markets has decided to declare that ‘fast market’ rules will apply to the Swedish and Finnish derivatives markets effective Monday June 27, 2016 and will be valid until further notice.
Fast market implies changes to the ‘Cancellation and price adjustment of erroneous transactions’ rule and to the Market Maker obligations.
For cancellation and price adjustment rules during ‘fast market’ see section 2.A.11.16 under the Nasdaq derivatives markets rules.
http://business.nasdaq.com/Docs/chapter-2_exchange-rules.pdf
Regarding Market Maker obligations during ‘fast market’, Market Makers are allowed to use double the spread stated in the obligations.