Exposing cleric somewhere in London (9)
I believe the answer is:
revealing
'exposing' is the definition.
('reveal' can be a synonym of 'expose')
'cleric somewhere in london' is the wordplay.
'cleric' becomes 'rev' (abbreviation for Reverend).
'somewhere in london' becomes 'ealing' (I've seen this in other clues).
'rev'+'ealing'='REVEALING'
(Other definitions for revealing that I've seen before include "Divulging" , "to be telltale" , "Discovering" , "Exposing" , "Disclosing" .)