Conservative faction left in party raised barrier (3,5)
I believe the answer is:
old guard
'conservative faction' is the definition.
(older and more conservative members of a group)
'left in party raised barrier' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'party' becomes 'do' (do is a kind of party).
'raised' is a reversal indicator.
'barrier' becomes 'guard'.
'l' going within 'do' is 'dlo'.
'dlo' back-to-front is 'old'.
'old'+'guard'='OLD GUARD'
(Other definitions for old guard that I've seen before include "Most conservative members of a group - of sentries" , "Dinosaurs" , "Conservative element; dyed-in-the-wool types" , "who may recall what railways used to be like" , "Long-standing group members, set in their ways" .)