Culturally pretentious leader dismissed from political group (4)
I believe the answer is:
arty
'culturally pretentious' is the definition.
(I've seen this in another clue)
'leader dismissed from political group' is the wordplay.
'leader dismissed from' means to remove the first letter.
'political group' becomes 'party' (a political party).
'party' with its first letter taken away is 'ARTY'.
(Other definitions for arty that I've seen before include "Keen on cultural matters" , "aspiring to be creative?" , "Affectedly interested in creative pursuits" , "Affectedly pretentious" , "Dilettante" .)