Socialists in Labour remaining? (4)
I believe the answer is:
left
This clue is a triple definition!
'socialists' is the first definition.
'in' acts as a link.
'labour' is the second definition.
(I've seen this in other clues)
'remaining?' is the third definition.
(synonyms)
(Other definitions for left that I've seen before include "not consumed" , "Departed, went away" , "One < side" , "quit" , "Punch, perhaps" .)