Pleasantly plump Conservative partner (6)
I believe the answer is:
chubby
'pleasantly plump' is the definition.
(I've seen this before)
'conservative partner' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'partner' becomes 'hubby' (informal term for husband).
'c'+'hubby'='CHUBBY'
(Other definitions for chubby that I've seen before include "Plumb and round" , "with some corporation?" , "Overweight" , "Round and pleasantly plump" , "Plump, rounded" .)