Blagged with prisoner (3)
I believe the answer is:
lag
'prisoner' is the definition.
(slang term)
'blagged with' is the wordplay.
'with' indicates a hidden word.
'LAG' is hidden within 'blagged'.
(Other definitions for lag that I've seen before include "trail" , "Drag one's feet" , "Wrap to protect from frost" , "Fall behind or cover to prevent heat loss" , "Hang back" .)