Bitter about Conservative purge (5)
I believe the answer is:
scour
'purge' is the definition.
(I know that purge can be written as scour)
'bitter about conservative' is the wordplay.
'bitter' becomes 'sour' (I've seen this before).
'about' means one lot of letters goes inside another.
'conservative' becomes 'C' (UK political abbreviation).
'sour' enclosing 'c' is 'SCOUR'.
(Other definitions for scour that I've seen before include "flush out" , "Clean by scrubbing" , "Scrub clean" , "Rub hard or search thoroughly" , "Scrub hard" .)