Universal anger about politician becoming mediator (6)
I believe the answer is:
umpire
'mediator' is the definition.
(thesaurus)
'universal anger about politician' is the wordplay.
'universal' becomes 'U' (film certificate).
'anger' becomes 'ire' (ire is intense rage).
'about' means one lot of letters go next to another.
'politician' becomes 'MP' (Member of Parliament).
'ire' after 'mp' is 'mpire'.
'u'+'mpire'='UMPIRE'
'becoming' acts as a link.
(Other definitions for umpire that I've seen before include "Impartial supervisor" , "Kind of referee as in cricket" , "The ref in cricket match" , "Official at a cricket match" , "Person enforcing rules" .)