Entry of one political party that's mean (6)
I believe the answer is:
inflow
'entry' is the definition.
(inflow can mean entry or coming in)
'one political party that's mean' is the wordplay.
'one' becomes 'i' (Roman numeral).
'political party' becomes 'NF' (National Front).
'that's mean' becomes 'low' (both can mean nasty or dishonourable).
'i'+'nf'+'low'='INFLOW'
'of' acts as a link.
(Other definitions for inflow that I've seen before include "Movement towards the centre" , "Arrival of air or water" , "Island of Tanzania" , "Rate of arrival" , "People arriving, say" .)