Leave vote to break up European appeal (4)
I believe the answer is:
exit
'leave' is the definition.
(I know that leave can be written as exit)
'vote to break up european appeal' is the wordplay.
'vote' becomes 'x' (how votes are marked).
'to break up' is an insertion indicator (inserted letters break up or split the word).
'european' becomes 'E' (abbreviation e.g. EU).
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'e'+'it'='eit'
'x' placed inside 'eit' is 'EXIT'.
(Other definitions for exit that I've seen before include "Way to leave" , "Escape route?" , "Sudden rush of pleasure" , "Depart" , "Way out sign" .)