Smashing police officer (5)
I believe the answer is:
super
This clue is a double definition.
'smashing' is the first definition.
(both can very good)
'police officer' is the second definition.
(term for a senior police officer)
(Other definitions for super that I've seen before include "(Of product) of extra fine quality" , "Informally great, really up there" , "Informally excellent, terrific" , "Gushily great, excellent" , "Great; wonderful" .)