The Zinoviev Letter
In October 1924 the MI5 intercepted a letter signed by Grigory Zinoviev, chairman of the Comintern in the Soviet Union, and Arthur McManus, the British representative on the committee. In the letter British communists were urged to promote revolution through acts of sedition. Vernon Kell, head of MI5 and Sir Basil Thomson head of Special Branch, were convinced that the letter was genuine. Kell showed the letter to Ramsay MacDonald, the Labour Prime Minister. It was agreed that the letter should be kept secret but someone leaked news of the letter to the Times and the Daily Mail.
The letter was published in these newspapers four days before the 1924 General Election and contributed to the defeat of MacDonald and the Labour Party. After the election it was claimed that two of MI5's agents, Sidney Reilly and Arthur Maundy Gregory, had forged the letter and that Major Joseph Ball (1885-1961), a MI5 officer, leaked it to the press. In 1927 Ball went to work for the Conservative Central Office where he pioneered the idea of spin-doctoring.
Research carried out by Gill Bennett in 1999 suggested that there were several MI5 and MI6 officers attempting the bring down the Labour Government in 1924, including