A UK citizen in a place with many races (5)
I believe the answer is:
ascot
'a place with many races' is the definition.
(Ascot is a racecourse)
'a uk citizen' is the wordplay.
'uk citizen' becomes 'scot' (someone from Scotland in the UK).
'a'+'scot'='ASCOT'
'in' is the link.
(Other definitions for ascot that I've seen before include "Royal race meeting venue" , "English racecourse in Berkshire" , "Racecourse with royal associations" , "prestigious meeting" , "sporting event" .)