Ample evidence of debt impounded by police (7)
I believe the answer is:
copious
'ample' is the definition.
('copious' can be a synonym of 'ample')
'evidence of debt impounded by police' is the wordplay.
'evidence of debt' becomes 'iou' (an IOU, 'I owe you').
'impounded by' indicates putting letters inside.
'police' becomes 'cops' (I've seen this before).
'iou' put within 'cops' is 'COPIOUS'.
(Other definitions for copious that I've seen before include "full" , "Ample" , "Abundant in supply" , "good measure" , "Providing loads of" .)