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In 1923, Winton entered Stowe School, which had just opened. He left without qualifications, attending night school while volunteering at the Midland Bank. He then went to Hamburg, where he worked at Behrens Bank, followed by Wasserman Bank in Berlin. In 1931, he moved to France and worked for the Banque Nationale de Crédit in Paris. He also earned a banking qualification in France. Returning to London, he became a broker at the London Stock Exchange. Though a stockbroker, Winton was also "an ardent socialist who became close to Labour Party luminaries Aneurin Bevan, Jennie Lee, and Tom Driberg". Through another socialist friend, Martin Blake, Winton became part of a left-wing circle opposed to appeasement and concerned about the dangers posed by the Nazis. At school, he had become an outstanding fencer, fencing both foil and epee, and was selected for the British team in 1938. He had hoped to compete in the following Olympics, but the games were canceled because of World War II