Conservative politician holding a party (4)
I believe the answer is:
camp
'party' is the definition.
(both can mean a group of people)
'conservative politician holding a' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'politician' becomes 'mp'.
'holding' indicates putting letters inside.
'c'+'mp'='cmp'
'cmp' placed around 'a' is 'CAMP'.
(Other definitions for camp that I've seen before include "Coterie" , "Ostentatiously gay" , "Gay - settlement" , "Military settlement" , "holiday location" .)