Go with Liberal Prime Minister (4)
I believe the answer is:
peel
'prime minister' is the definition.
(I've seen this before)
'go with liberal' is the wordplay.
'go' becomes 'pee' (both can mean to urinate**).
'with' is a charade indicator (letters next to each other).
'liberal' becomes 'l' (abbreviation).
'pee'+'l'='PEEL'
(Other definitions for peel that I've seen before include "PM once; remove skin" , "See 4 and 22" , "Citrus skin" , "A PM; a fortified tower" , "Strip; rind" .)