The French state's Eurosceptics (7)
I believe the answer is:
leavers
'eurosceptics' is the definition.
(people who campaigned for the UK to leave the EU)
'the french state's' is the wordplay.
'the french' becomes 'le' ('the' in French).
'state's' becomes 'avers' (both can mean to declare).
'le'+'avers'='LEAVERS'
(Other definitions for leavers that I've seen before include "People departing" , "They're off" , "Those exiting" , "Several (anag) -- Brexiteers" .)