The "Zinoviev letter" was a controversial document published by the British Daily Mail newspaper four days before the general election in 1924. It purported to be a directive from the Communist International in Moscow to the Communist Party of Great Britain. It said the resumption of diplomatic relations (by a Labour government) would hasten the radicalisation of the British working class. The letter took its name from the apparent signature of a senior Soviet official Grigory Zinoviev. The letter seemed authentic at the time but historians now believe it was a forgery. It called for intensified communist agitation in Britain. Historians now agree that the letter had little impact on the Labour vote—which held up in 1924. However, it aided the Conservative Party in hastening the collapse of the Liberal party that led to the Conservative landslide.A.J.P. Taylor argues that the most important impact was on the psychology of Labourites, who for years blamed their defeat on foul play, thereby misunderstanding the political forces at work and postponing needed reforms in the Labour Party.
In 1924, the socialist Labour Party formed a government for the first time. However, it was a minority government, and was liable to fall if the Conservatives and Liberals combined against it. In foreign policy, the government recognised the Soviet Union in February 1924, and proposed to lend it money. On 8 October 1924, the Labour government of Ramsay MacDonald suffered defeat in the House of Commons on a motion of no confidence, forcing MacDonald to go to the King to seek a dissolution of Parliament and new elections. The immediate cause of the parliamentary defeat had been the government's decision to drop the prosecution of communist editor John Ross Campbell under the Incitement to Mutiny Act 1797 for publication of an open letter in Workers Weekly calling on soldiers to "let it be known that, neither in the class war nor in a military war, will you turn your guns on your fellow workers." New national elections were scheduled for 29 October.