A great deal contributed within limits of policy (6)
I believe the answer is:
plenty
'a great deal' is the definition.
(I know that great deal can be written as plenty)
'contributed within limits of policy' is the wordplay.
'contributed' becomes 'lent' ('lend' can be a synonym of 'contribute').
'within' is an insertion indicator.
'limits of' means to remove the middle letters.
'policy' with its centre removed is 'py'.
'lent' going into 'py' is 'PLENTY'.
(Other definitions for plenty that I've seen before include "A full supply - lots" , "Amplitude or abundance" , "A lot" , "As much as necessary" , "More than enough" .)