Conservative, one departing in a chopper (7)
I believe the answer is:
cleaver
'a chopper' is the definition.
('cleaver' can be a synonym of 'chopper')
'conservative one departing' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'one departing' becomes 'leaver' (I've seen this before).
'c'+'leaver'='CLEAVER'
'in' acts as a link.
(Other definitions for cleaver that I've seen before include "A butcher's chopping tool" , "Butcher's chopper" , "Meat axe" , "A clever sort of axe" , "dangerous object?" .)