Artist in private room, Bobby (4,9)
I believe the answer is:
john constable
'artist' is the definition.
(English painter)
'private room bobby' is the wordplay.
'private room' becomes 'john' (slang term for toilet).
'bobby' becomes 'constable' (bobby can informally mean a police officer).
'john'+'constable'='JOHN CONSTABLE'
'in' is the link.
(Other definitions for john constable that I've seen before include "English landscape painter, d. 1837" , "Haywain artist" .)