Claim a member to be in drink (6)
I believe the answer is:
allege
'claim' is the definition.
(to allege something is to make a claim)
'a member to be in drink' is the wordplay.
'a member' becomes 'leg' (member can mean a limb).
'to be in' is an insertion indicator.
'drink' becomes 'ale' (type of beer).
'leg' inserted inside 'ale' is 'ALLEGE'.
(Other definitions for allege that I've seen before include "hold" , "Cite in discussion" , "Aver (without proof)" , "Claim, suggest" , "Swear" .)