Posh politician one socialist judged (7)
I believe the answer is:
umpired
'judged' is the definition.
(umpiring is a kind of judging)
'posh politician one socialist' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'politician' becomes 'mp' (Member of Parliament).
'one' becomes 'i' (roman numeral).
'socialist' becomes 'red' (red is a kind of socialist).
'u'+'mp'+'i'+'red'='UMPIRED'
(Other definitions for umpired that I've seen before include "Refereed" , "Officiated (cricket)" , "Ripe mud (anag.)" .)