Blagged about prisoner (3)
I believe the answer is:
lag
'prisoner' is the definition.
(slang term)
'blagged about' is the wordplay.
'about' indicates a hidden word (the clue goes around or about the answer).
'LAG' can be found hidden inside 'blagged'.
(Other definitions for lag that I've seen before include "Drop behind" , "Delay" , "Ex-convict" , "Wrap to protect from frost" , "Convict (slang)" .)