Postwar prime minister (6)
I believe the answer is:
attlee
'postwar prime minister' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for attlee that I've seen before include "Former British PM" , "Prime minister nineteen forty five to fifty one" , "Clement --, former PM" , "Labour prime minister, d. 1967" , "British PM, 1945-51" .)