Final answer:
Winston Churchill was the Prime Minister of Britain during the Second World War, who took office after Neville Chamberlain's resignation in 1940 and led the nation against Nazi Germany.
Step-by-step explanation:
The Prime Minister of Britain during the Second World War was Winston Churchill. He was a lifelong British politician who was acutely aware of the threats posed by Adolf Hitler's rise to power in Germany. After Neville Chamberlain resigned in 1940, Churchill stepped in as Prime Minister and led Britain through the arduous fight against Nazi Germany.
Churchill's leadership was characterized by his determination and iconic speeches, pledging to lead the country with the policy, "to wage war by sea, land and air with all our might," and famously stating, "I have nothing to offer but blood, toil, tears and sweat." He remained Prime Minister until the Potsdam Conference in July 1945, when Clement Attlee succeeded him after the Labour party's victory in the general election.