Release a Conservative and resign (6)
I believe the answer is:
acquit
'release' is the definition.
(I've seen this before)
'a conservative and resign' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'and' is a charade indicator (letters next to each other).
'resign' becomes 'quit' (to quit something is to resign from it).
'a'+'c'+'quit'='ACQUIT'
(Other definitions for acquit that I've seen before include "Discharge from court - not guilty" , "Group of families" , "Discharge as innocent, dismiss charge" , "Free from captivity, being innocent" , "Free (from charge)" .)