Belonging to 'chosen', a Tory politician (7)
I believe the answer is:
senator
'politician' is the definition.
(I've seen this before)
'belonging to chosen a tory' is the wordplay.
'belonging to' says the answer is hidden in the clue (I've seen this in other clues).
'SENATOR' is hidden in the letters of 'chosen a tory'.
(Other definitions for senator that I've seen before include "US/Roman politician" , "Member of upper house of legislature" , "One from uni's governing body" , "eg Bob Dole" , "Clinton, perhaps" .)