Politician surrounded by drink in plenty (5)
I believe the answer is:
ample
'in plenty' is the definition.
(thesaurus)
'politician surrounded by drink' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'surrounded by' is an insertion indicator.
'drink' becomes 'ale' (type of beer).
'mp' put inside 'ale' is 'AMPLE'.
(Other definitions for ample that I've seen before include "Plenteous" , "Large, accommodating" , "Easily sufficient" , "Plentiful; large" , "Quite sufficient, more than enough" .)