Coldness at the heart of policemen (3)
I believe the answer is:
ice
'coldness' is the definition.
(ice can mean coldness or hostility)
'the heart of policemen' is the wordplay.
'the heart of' indicates a hidden word.
'ICE' can be found hidden inside 'policemen'.
'at' is the link.
(Other definitions for ice that I've seen before include "Diamonds (informal)" , "Slippery surface" , "Decorate a cake" , "Diamonds (sl)" , "Girl's best friends" .)