Tool for hard labour damaged hedge in prison (12)
I believe the answer is:
sledgehammer
'tool' is the definition.
(sledgehammer is a kind of tool)
'damaged hedge in prison' is the wordplay.
'damaged' indicates anagramming the letters.
'in' is an insertion indicator.
'prison' becomes 'slammer' (I've seen this before).
'hedge' with letters rearranged gives 'edgeh'.
'edgeh' going inside 'slammer' is 'SLEDGEHAMMER'.
'for hard labour' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sledgehammer that I've seen before include "Dealer of heavy blow" , "One may be used to break rocks" , "Unsubtle" , "One violently smashing" , "Big hitter" .)