Elected Conservative ringing male on paper (2,6)
I believe the answer is:
in theory
'on paper' is the definition.
(synonyms)
'elected conservative ringing male' is the wordplay.
'elected' becomes 'in' (in government).
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'ringing' is an insertion indicator.
'male' becomes 'he' (he refers to a man).
'tory' placed around 'he' is 'theory'.
'in'+'theory'='IN THEORY'
(Other definitions for in theory that I've seen before include "In principal" , "Ideally" , "according to the assumed facts" , "On paper" .)