Spoke about Conservative, one who favours extreme change (7)
I believe the answer is:
radical
'one who favours extreme change' is the definition.
'spoke about conservative' is the wordplay.
'spoke' becomes 'radial' (I've seen this before).
'about' is an insertion indicator.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'radial' enclosing 'c' is 'RADICAL'.
(Other definitions for radical that I've seen before include "Fundamental - thoroughgoing" , "'Revolutionary, extremist (7)'" , "Complete" , "Militant" , "Going to the root" .)