It's great to be a policeman (5)
I believe the answer is:
super
I believe this clue is a double definition.
'it's great' is the first definition.
(both can mean excellent)
'a policeman' is the second definition.
(short for superintendant)
'to be' is the link.
(Other definitions for super that I've seen before include "Marvellous, terrific" , "Informally excellent, terrific" , "Informally terrific, splendid" , "of high quality" , "Gushily great, excellent" .)