Billion pounds possibly for sponsors (7)
I believe the answer is:
backers
'for sponsors' is the definition.
(backer is a kind of sponsor)
'billion pounds possibly' is the wordplay.
'billion' becomes 'b'.
'pounds possibly' becomes 'ackers' (ackers can informally mean money).
'b'+'ackers'='BACKERS'
(Other definitions for backers that I've seen before include "coping with reverses?" , "Angels" .)