Approach faction in British Left (8)
I believe the answer is:
nearside
'british left' is the definition.
(left side of the road in Britain)
'approach faction' is the wordplay.
'approach' becomes 'near' (synonyms).
'faction' becomes 'side' (one side in a conflict or controversy).
'near'+'side'='NEARSIDE'
'in' acts as a link.
(Other definitions for nearside that I've seen before include "left in the UK" , "Part of vehicle closest to the kerb" , "On which one finds passenger" , "left by kerb?" , "Vehicle's left (in Britain)" .)