Radical cusses about Conservative win (7)
I believe the answer is:
success
'win' is the definition.
(thesaurus)
'radical cusses about conservative' is the wordplay.
'radical' is an anagram indicator.
'about' is an insertion indicator.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'cusses' anagrammed gives 'sucess'.
'sucess' going around 'c' is 'SUCCESS'.
(Other definitions for success that I've seen before include "It breeds itself, it's said" , "The attainment of fame or wealth" , "Hit" , "Positive result; celebrity" , "The accomplishment of an aim" .)