Battle not started by English postwar prime minister (6)
I believe the answer is:
attlee
'postwar prime minister' is the definition.
(I've seen this in another clue)
'battle not started by english' is the wordplay.
'not started' means to remove the first letter.
'by' says to put letters next to each other.
'english' becomes 'E' (abbreviation).
'battle' with its first letter removed is 'attle'.
'attle'+'e'='ATTLEE'
(Other definitions for attlee that I've seen before include "5,27 [PRIME MINISTER]" , "Post-war leader" , "British PM, 1945-51" , "Labour PM" , "Old statesman" .)