Liberal in Amersham pledge (5)
I believe the answer is:
ample
'liberal' is the definition.
(I've seen this in another clue)
'in amersham pledge' is the wordplay.
'in' indicates the answer is hidden within the clue.
'AMPLE' is hidden in the letters of 'amersham pledge'.
(Other definitions for ample that I've seen before include "Plenteous" , "Big" , "Large enough" , "Liberal" , "Quite sufficient, more than enough" .)