Liberal member getting stuck into beer (5)
I believe the answer is:
ample
'liberal' is the definition.
(I've seen this in other clues)
'member getting stuck into beer' is the wordplay.
'member' becomes 'MP' (Member of Parliament).
'getting stuck into' means one lot of letters goes inside another.
'beer' becomes 'ale' (type of beer).
'mp' inserted inside 'ale' is 'AMPLE'.
(Other definitions for ample that I've seen before include "Copious - abundant" , "Adequate" , "Plenteous" , "No more, please!" , "Sealed glass container for dose of medicine" .)