Extremist possibly drawing back following united labour front (5)
I believe the answer is:
ultra
'extremist' is the definition.
(ultra can mean an extremist or radical)
'drawing back following united labour front' is the wordplay.
'drawing' becomes 'art' (drawing is an art).
'back' says the letters should be written in reverse.
'following' says to put letters next to each other.
'front' suggests taking the first letters.
The initial letters of 'united labour' is 'ul'.
'art' reversed gives 'tra'.
'tra' after 'ul' is 'ULTRA'.
'possibly' acts as a link.
(Other definitions for ultra that I've seen before include "Extreme - extremist" , "Immoderate" , "Prefix meaning beyond or extremely" , "Project started at Bletchley Park in 1939 to break the Enigma code" , "Prefix meaning excessively or extremely" .)