Politically extreme? No Conservative spoke (6)
I believe the answer is:
radial
'spoke' is the definition.
(I've seen this before)
'politically extreme? no conservative' is the wordplay.
'politically extreme?' becomes 'radical' (I've seen this before).
'no' suggests deleting specific letters.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'radical' with 'c' taken out is 'RADIAL'.
(Other definitions for radial that I've seen before include "tire (American)" , "tread on it" , "Having spokes that branch out from a centre" , "a sort of drill" , "Kind of pneumatic tyre" .)