British intelligence personnel who defected to the Soviet Union

Guy Francis de Moncy Burgess (16 April 1911 – 30 August 1963) was a British diplomat and Soviet agent, a member of the Cambridge Five spy ring that operated from the mid-1930s to the early years of the Cold War era. His defection in 1951 to the Soviet Union, with his fellow spy Donald Maclean, led to a serious breach in Anglo-United States intelligence co-operation, and caused long-lasting disruption and demoralisation in Britain's foreign and diplomatic services.

Harold Adrian Russell "Kim" Philby (1 January 1912 – 11 May 1988) was a British intelligence officer and a double agent for the Soviet Union. In 1963 he was revealed to be a member of the Cambridge Five, a spy ring which passed information to the Soviet Union during World War II and in the early stages of the Cold War. Of the five, Philby is believed to have been most successful in providing secret information to the Soviets.

Donald Duart Maclean (25 May 1913 – 6 March 1983) was a British diplomat and member of the Cambridge Five spy ring which conveyed government secrets to the Soviet Union.

George Blake (born George Behar, 11 November 1922 – 26 December 2020) was a former British spy who worked as a double agent for the Soviet Union. He became a Communist and decided to work for the KGB while a prisoner during the Korean War. Discovered in 1961 and sentenced to 42 years in prison, he escaped from Wormwood Scrubs prison in 1966 and fled to the Soviet Union. He was not one of the Cambridge Five spies, although he associated with Donald Maclean and Kim Philby after reaching the Soviet Union.