Prison critic? (7)
I believe the answer is:
slammer
I believe this clue is a double definition.
'prison' is the first definition.
(I know that slammer is a type of prison)
'critic?' is the second definition.
(someone who slams or criticises)
(Other definitions for slammer that I've seen before include "One criticising, as it were" , "One severely criticises" , "Prison - critic?" , "cocktail?" , "He noisily leaves the room" .)