Bloke largely innocent, on reflection, but keeping the truth hidden (5-2)
I believe the answer is:
'keeping the truth hidden' is the definition.
(a cover-up hides the truth)
'bloke largely innocent on reflection' is the wordplay.
'bloke' becomes 'cove' (both can informally mean a man).
'largely' means to remove the last letter.
'innocent' becomes 'pure' (I've seen this in another clue).
'on reflection' shows that the letters should be reversed in order.
'pure' with its final letter taken away is 'pur'.
'pur' written backwards gives 'rup'.
'but' is the link.
(Other definitions for cover-up that I've seen before include "Concealments of facts - work for tribunals" , "An attempt to conceal the truth" , "Conspiracy to conceal" , "Whitewash" , "Withhold information" .)