Blow cover revealing criminal record (3,5)
I believe the answer is:
rap sheet
'criminal record' is the definition.
(a rap sheet is a police record)
'blow cover' is the wordplay.
'blow' becomes 'rap' (rap is a kind of blow).
'cover' becomes 'sheet' (sheeting is a kind of covering).
'rap'+'sheet'='RAP SHEET'
'revealing' is the link.
(Other definitions for rap sheet that I've seen before include "Where to find previous" , "record of arrests" , "'Written record of charges (3,5)'" , "Criminal record, colloquially" .)