Flog; party official (4)
I believe the answer is:
whip
This clue is a double definition.
'flog' is the first definition.
(synonyms)
'party official' is the second definition.
(I've seen this before)
(Other definitions for whip that I've seen before include "Political officer who ensures party members attend and vote" , "Lash - political disciplinarian" , "Lash for driving animals" , "Flog - pinch" , "Beat (cream)" .)