Terrible derision about politician behind bars (10)
I believe the answer is:
imprisoned
'behind bars' is the definition.
(I've seen this before)
'terrible derision about politician' is the wordplay.
'terrible' indicates an anagram.
'about' is an insertion indicator.
'politician' becomes 'mp'.
'derision' with letters rearranged gives 'irisoned'.
'irisoned' enclosing 'mp' is 'IMPRISONED'.
(Other definitions for imprisoned that I've seen before include "Locked up" , "Put away" , "behind bars" , "in jail" .)