He had passed vetting procedures and was undetected for 15 years despite being an active Communist Party member who travelled to Russia, Bulgaria and Yugoslavia and had obvious access to cash.
In 1982 Geoffrey Prime was jailed for 35 years for selling to the KGB top-secret information obtained from the GCHQ electronic surveillance centre at Cheltenham.
In the same period Michael Bettaney, an MI5 officer, was also exposed as a traitor for trying to offer information to the KGB in London.
It took many years for the activities of the Cambridge spy ring to come to light after the defection of MI5 officer Guy Burgess and Foreign Office diplomat Donald Maclean in 1951. Kim Philby, a head of anti-Communist counter-espionage, was able to flee to Russia in 1963. Not until 1979 was Anthony Blunt identified as the fourth man.
Cathy Massiter, an ex-MI5 officer, gave a television interview in 1985 in which she described how the agency spied on trade union leaders, members of the Campaign for Nuclear Disarmament and other left-wing activists.
Two years later, after a wrangle over his pension, ex-MI5 officer Peter Wright published Spycatcher, describing how he "bugged and burgled" his way across London and how M15 plotted against Harold Wilson.
Richard Tomlinson, who was dismissed from MI6 and not allowed to take his case to an industrial tribunal, went to a newspaper with an account of his work with the intelligence services.
David Shayler, a former M15 officer, also went to the press with allegations of a plot by British intelligence to kill Colonel Gaddafi, the Libyan leader.Reuse content