Party in lead is Conservative (5)
I believe the answer is:
disco
'party' is the definition.
(dance party)
'in lead is conservative' is the wordplay.
'in' indicates the answer is hidden within the clue.
'DISCO' can be found hidden inside 'lead is conservative'.
(Other definitions for disco that I've seen before include "Dancehall with recorded music, in short" , "Type of music" , "Modern dancehall of youth" , "Dance party" , "1970s' musical genre" .)