Turncoats of course (5)
I believe the answer is:
ascot
This might be a double definition.
'turncoats of' is the first definition.
The definition suggests a singular noun which matches the answer.
'course' is the second definition.
(Ascot is a racecourse)
(Other definitions for ascot that I've seen before include "Tie round the neck" , "sporting venue" , "Where the Queen often sees racehorses" , "Coats (anag) - racecourse" , "Where ladies wear new hats" .)