40s British prime minister (6)
I believe the answer is:
attlee
''40s british prime minister' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for attlee that I've seen before include "Labour prime minister, d. 1967" , "Post-war leader" , "Labour PM" , "Prime minister, 1945-51" , "British PM, 1945-51" .)