British PM's never-ending conflict (6)
I believe the answer is:
battle
'conflict' is the definition.
(I know that conflict can be written as battle)
'british pm's never-ending' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'pm' becomes 'attlee' (prime minister Clement Attlee).
'never ending' means to remove the last letter.
'attlee' with its final letter taken away is 'attle'.
'b'+'attle'='BATTLE'
(Other definitions for battle that I've seen before include "Eg, Bosworth, Blenheim" , "Difficult conflict or struggle" , "Sustained conflict" , "Military conflict" , "Lengthy conflict" .)