The Zinoviev letter was a fake document published and sensationalised by the British Daily Mail newspaper four days before the 1924 United Kingdom general election, which was held on 29 October. The letter purported to be a directive from Grigory Zinoviev, the head of the Communist International (Comintern) in Moscow, to the Communist Party of Great Britain (CPGB), ordering it to engage in seditious activities. It stated that the normalisation of British–Soviet relations under a Labour Party government would radicalise the British working class and put the CPGB in a favourable position to pursue a Bolshevik-style revolution. It further suggested that these effects would extend throughout the British Empire. The right-wing press depicted the letter as a grave foreign subversion of British politics and blamed the incumbent Labour government under Ramsay MacDonald for promoting the policy of political reconciliation and open trade with the Soviet Union on which the scheme appeared to depend. The election resulted in the fall of the first Labour government and a strong victory for the Conservative Party and the continued collapse of the Liberal Party. Labour supporters often blamed the letter, at least in part, for their party's defeat.

The Daily Mail is a British daily middle-market tabloid newspaper published in London. It was founded in 1896. As of 2020, it was the highest paid circulation newspaper in the UK. Its sister paper The Mail on Sunday was launched in 1982, a Scottish edition was launched in 1947, and an Irish edition in 2006. Content from the paper appears on the MailOnline news website, although the website is managed separately and has its own editor.