Postgate's anti-fascism led him to move away from his earlier pacifism. Postgate supported the Second World War and joined the Home Guard near his home in Finchley, London.Brock and Young, pp.209.Postgate & Postgate, pp. 213–215 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.Postgate & Postgate, pp. 243–254 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.
