Guru's morning in Westminster? (5)
I believe the answer is:
swami
'guru's' is the definition.
(I've seen this before)
'morning in westminster?' is the wordplay.
'morning' becomes 'am'.
'in' means one lot of letters goes inside another.
'westminster?' becomes 'swi' (resembles SW1, London postcode).
'am' put inside 'swi' is 'SWAMI'.
(Other definitions for swami that I've seen before include "Teacher abroad" , "Religious master" , "Hindu mystic" , "Hindu male religious teacher" , "Indian religious teacher" .)