Does no work - did less after blowing cover (5)
I believe the answer is:
idles
'does no work' is the definition.
(idle can mean to do very little work)
'did less after blowing cover' is the wordplay.
'after blowing cover' says the answer is hidden in the clue (the answer must be uncovered within the clue).
'IDLES' is hidden in the letters of 'did less'.
(Other definitions for idles that I've seen before include "Spends time doing nothing" , "Of engine, just ticks over in neutral" , "Wastes time" , "Avoids working" , "Lazes around" .)