Conservative member has chosen to become a monk (9)
I believe the answer is:
carmelite
'a monk' is the definition.
(carmelite is a type of monk)
'conservative member has chosen' is the wordplay.
'conservative' becomes 'C' (UK political abbreviation).
'member' becomes 'arm' (member can mean a limb).
'has' says to put letters next to each other.
'chosen' becomes 'elite' (I've seen this before).
'c'+'arm'+'elite'='CARMELITE'
'to become' is the link.
(Other definitions for carmelite that I've seen before include "Prayer" , "Does Mal recite about the monk?" , "Sister" , "Friar or nun of particular order" , "member of religious order" .)