The Cambridge Spy Ring was a ring of spies in the United Kingdom that passed information to the Soviet Union during World War II and was active from the 1930s until at least into the early 1950s. None were ever prosecuted for spying. The number and membership of the ring emerged slowly from the 1950s onwards. As far as the general public was concerned, this started with the sudden flight of Donald Maclean (cryptonym: Homer) and Guy Burgess (cryptonym: Hicks) to the Soviet Union in 1951. Suspicion immediately fell on Harold "Kim" Philby (cryptonyms: Sonny, Stanley), but he did not defect until 1963. Anthony Blunt (cryptonyms: Tony, Johnson) and John Cairncross (cryptonym: Liszt), the last two of the group, confessed to British intelligence but this remained a secret for many years, until 1979 for Anthony Blunt and 1990 for John Cairncross. In time the Cambridge Four evolved to become the Cambridge Five. In the innermost circles of the KGB, they were supposedly dubbed as the Magnificent Five.
The term "Cambridge" refers to the recruitment of the group during their education at the University of Cambridge in the 1930s. Debate surrounds the exact timing of their recruitment by Soviet intelligence; Anthony Blunt claimed that they were not recruited as agents until they had graduated. Blunt, a Fellow of Trinity College, was several years older than Burgess, Maclean, and Philby; he acted as a talent-spotter and recruiter for the group save Burgess.All of the five were convinced that the Marxism–Leninism of Soviet Communism was the best available political system, and especially the best defence against the rise of fascism. All pursued successful careers in branches of the British government. They passed large amounts of intelligence to the Soviet Union, so much so that the KGB became suspicious that at least some of it was false. Perhaps as important as the intelligence they passed was the demoralizing effect to the British Establishment of their slow unmasking, and the mistrust in British security this caused in the United States.
Many others have also been accused of membership in the Cambridge ring. Blunt and Burgess were both members of the Cambridge Apostles, an exclusive secret society at Cambridge University. Other Apostles accused of having spied for the Soviets include Michael Straight and Guy Liddell.