The British intelligence coordinating committee created in January 1941 to supervise the management of MI5’s double agents and give approval to information being passed to the enemy. The name comes from the Roman numeral XX, a visual pun on “double cross.” The XX Committee met weekly and was chaired by J. C. Masterman, his secretary being another MI5 officer, John Marriott. The other membership was made up of staff transferred from the Home Defence Security Executive, the Secret Intelligence Service, and the directors of military intelligence, naval intelligence, and the Home Forces.
During the course of World War II, the XX Committee met weekly 226 times and oversaw the operations of more than 40 controlled enemy agents until it was dissolved in December 1944. The existence of the XX Committee was revealed publicly in 1972 with the publication by Sir John Masterman of The Double Cross System of the War of 1939–45, a slightly abridged version of an account he had been commissioned to write for the Security Service in 1945.