Revolutionary spoke about Conservative (7)
I believe the answer is:
radical
'revolutionary' is the definition.
('radical' can be a synonym of 'revolutionary')
'spoke about conservative' is the wordplay.
'spoke' becomes 'radial' (I've seen this before).
'about' indicates putting letters inside.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'radial' going around 'c' is 'RADICAL'.
(Other definitions for radical that I've seen before include "Total" , "One with rooted" , "Deep-seated" , "Innovative, progressive" , "Tending towards extreme political views" .)