A politician engaged in diatribe, unrestrained (7)
I believe the answer is:
rampant
'unrestrained' is the definition.
(thesaurus)
'a politician engaged in diatribe' is the wordplay.
'politician' becomes 'mp'.
'engaged in' is an insertion indicator.
'diatribe' becomes 'rant' (I've seen this in other clues).
'a'+'mp'='amp'
'amp' going into 'rant' is 'RAMPANT'.
(Other definitions for rampant that I've seen before include "Spreading unchecked" , "Fulminate" , "Unchecked (and violent?)" , "On the rampage" , "Unrestrained and violent" .)