Politician's wrong reason to go round the West End (7)
I believe the answer is:
senator
'politician's' is the definition.
(senator is a kind of politician)
'wrong reason to go round the west end' is the wordplay.
'wrong' indicates an anagram.
'to go round' means one lot of letters goes inside another.
'end' says to take the final letters.
The final letter of 'west' is 't'.
'reason' is an anagram of 'senaor'.
'senaor' enclosing 't' is 'SENATOR'.
(Other definitions for senator that I've seen before include "American politician" , "Member of the Upper House of the US Congress" , "One of 100 on Capitol Hill" , "Treason committed by member of Upper House" , "One from uni's governing body" .)