Awfully nice cover for an operative (2,5)
I believe the answer is:
in force
'an operative' is the definition.
(I've seen this before)
'awfully nice cover for' is the wordplay.
'awfully' is an anagram indicator.
'cover' is an insertion indicator.
'nice' is an anagram of 'ince'.
'ince' going around 'for' is 'IN FORCE'.
(Other definitions for in force that I've seen before include "Legally operative" , "(Of law) legally binding" , "as a copper?" , "Bobby is" , "policemen are" .)