Policeman and doctor let loose (7)
I believe the answer is:
mountie
'policeman' is the definition.
(Mountie is an example)
'doctor let loose' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'let loose' becomes 'untie' (I've seen this before**).
'mo'+'untie'='MOUNTIE'
'and' is the link.
(Other definitions for mountie that I've seen before include "Canadian policemen" , "North American policeman" , "Canadian police officer" , "The lawman always gets his man!" , "Canadian cop on a horse?" .)