In 1940, Pritt was expelled from the Labour Party for defending the Soviet invasion of Finland. His book "Must the War Spread?" sympathized with the Soviets and led him to be greatly disliked by the Labour Party elite during and after the war. After 1940, he sat as an Independent Labour member, and at the 1945 general election was re-elected in Hammersmith North under that label gaining a 63% share of the vote against official Labour and Conservative candidates. In 1949 he formed the Labour Independent Group with four other fellow travellers, including John Platts-Mills and Konni Zilliacus, who had also been expelled from the Labour Party for pro-Soviet sympathies. At the general election of 1950, all the members of the Labour Independent Group lost their seats. By this time, Pritt's opposition to the Cold War and NATO had made him an "unpopular figure" in Britain.