Instance of former member overcome by drink (7)
I believe the answer is:
example
'instance' is the definition.
(I know that instance can be written as example)
'former member overcome by drink' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'member' becomes 'MP' (Member of Parliament).
'overcome by' is an insertion indicator.
'drink' becomes 'ale' (type of beer).
'mp' put into 'ale' is 'ample'.
'ex'+'ample'='EXAMPLE'
'of' is the link.
(Other definitions for example that I've seen before include "Fact that illustrates a general rule" , "lesson" , "Specimen, illustration" , "Something to be imitated" , "Thing illustrating a general rule" .)