Rose when Conservative finished (8)
I believe the answer is:
ascended
'rose' is the definition.
('ascend' can be a synonym of 'rise')
'when conservative finished' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'conservative' becomes 'C' (UK political abbreviation).
'finished' becomes 'ended' (similar in meaning).
'as'+'c'+'ended'='ASCENDED'
(Other definitions for ascended that I've seen before include "Climbed, went up" , "R [ROSE]" .)