A hack drinking policeman's drink (7)
I believe the answer is:
alcopop
'drink' is the definition.
(type of alcoholic drink)
'a hack drinking policeman's' is the wordplay.
'hack' becomes 'lop' (both can mean to cut up).
'drinking' is an insertion indicator.
'policeman' becomes 'cop' (slang term).
'lop' enclosing 'cop' is 'lcopop'.
'a'+'lcopop'='ALCOPOP'
(Other definitions for alcopop that I've seen before include "Mixed drink" , "A mix of alcohol and soft drink" , "Polo cap (anag.)" , "Liquor drink for kids" , "fizzy drink" .)