Postgate's anti-fascism led him to move away from his earlier pacifism. Postgate supported World War II and joined the Home Guard near his home in Finchley, London. In 1942 he obtained a post as a temporary Civil Servant in the wartime Board of Trade, concerned with the control of rationed supplies, and he remained in the Service for eight years. He continued his left wing writings, and his question-and-answer pamphlet "Why you Should Be A Socialist", widely distributed among the returning military as the war ended, probably contributed significantly to the Labour Party's post-war landslide victory.