Sick English prisoner: revolting criminal (7)
I believe the answer is:
illegal
'criminal' is the definition.
('illegal' can be similar in meaning to 'criminal')
'sick english prisoner revolting' is the wordplay.
'sick' becomes 'ill' ('ill' can be a synonym of 'sick').
'english' becomes 'e' (abbreviation).
'prisoner' becomes 'lag' (I've seen this before).
'revolting' says the letters should be written in reverse.
'lag' written backwards gives 'gal'.
'ill'+'e'+'gal'='ILLEGAL'
(Other definitions for illegal that I've seen before include "Against the rules" , "Black-market" , "Not lawful" , "Unlawful" , "crooked" .)