In the 1930s a number of young men at Cambridge University were recruited as Soviet spies. They became known by the KGB as the 'magnificent five' but were better known in Britain as the Cambridge spy ring.

They were not motivated by financial gain but by the belief that capitalism was corrupt and that the Soviet Union offered a better model for society.

The Cambridge spy ring was informally led by Harold 'Kim' Philby. He and his friends later moved into jobs in British Intelligence and the Foreign Office where they had access to top secret information. They spent their working lives passing valuable information to the Soviet Union.

Kim Philby was head of anti-Communist counter-espionage

Kim Philby (1912-1988) worked for British Intelligence from 1944-46 as head of anti-Communist counter-espionage. He also became secretary of the British embassy in Washington and worked with the CIA from 1949-1951. He later worked as a journalist in Beirut and in 1963 disappeared. It was later discovered he had moved to Russia where he had been granted citizenship.

Guy Burgess (1910-63) worked for the BBC from 1936-1939 and 1941-44. While working for the BBC in the 1940s he was also employed by MI5. Later moving to the Foreign Office he became a secretary under Kim Philby in Washington in 1950. Burgess was recalled from the US in 1950 for 'serious misconduct' and subsequently he and fellow spy Donald Maclean disappeared. They emerged in the Soviet Union a few years later. Burgess eventually died in Moscow.

Donald Maclean was warned by Philby that he was under suspicion

After his years at Cambridge Donald Maclean (1913-1983) joined the diplomatic service. In 1950 he became head of the American Department at the Foreign Office where he had access to top secret information on atomic development. Maclean was warned by Philby that he was under suspicion and he subsequently disappeared with Guy Burgess. He re-appeared in Russia in 1956. In 1979 it was revealed that he had escaped with the help of fellow spy Anthony Blunt.

Anthony Blunt was publicly revealed to be a Soviet spy in 1979

Anthony Blunt (1907-1983) acted as a talent scout supplying the names of possible recruits to the communist cause. During World War II he worked for British Intelligence. After the defection of Kim Philby in 1964 Blunt confessed his involvement in exchange for immunity from prosecution, but his role was not made public until 1979.

Also an art historian, Blunt continued in his role as surveyor of the Queen's pictures and Director of the Courtauld Institute of Art. When his full role the "fourth man" of the Cambridge spy ring was revealed in 1979 he was stripped of his knighthood and academic honours.

The identity of the mysterious fifth man that intelligence experts had suspected to be part of the spy ring was revealed in 1990.

John Cairncross leaked information about Bletchley Park

John Cairncross was spotted by Anthony Blunt at Cambridge and introduced to Guy Burgess. He was recruited to the Communist party in 1937 and worked in the Foreign Office alongside Donald Maclean.

While working at the Treasury he was able to leak details about the military decoding centre, Bletchley Park. Cairncross' information enabled Soviet spies to change their codes as British Intelligence were about to crack them.

His information about British and American atomic weapons programmes are thought to have been the foundation of the Soviet nuclear programme.