Shop returned waterproof coat missing (3,2)
I believe the answer is:
rat on
'shop' is the definition.
(both can mean to betray or inform upon)
'returned waterproof coat missing' is the wordplay.
'returned' says the letters should be written backwards.
'waterproof coat' becomes 'tar' (coat applied to roads).
'missing' becomes 'on' (I can't explain this - if you can you should give a lot more credence to this answer).
'tar' backwards is 'rat'.
'rat'+'on'='RAT ON'
(Other definitions for rat on that I've seen before include "Betray" , "Give away" , "grass up" , "shop" , "desert" .)