Spy story

True tales of treachery - stories of real spies, lies and the KGB

The most extensive and dangerous network ever uncovered was the Cambridge Five.

Recruited at the city's university, Guy Burgess, Donald Maclean, Anthony Blunt and Kim Philby worked their way into the heart of the establishment - while passing secrets to their Russian bosses.

The identity of the fifth Cambridge spy has never been revealed.

Thousands of confidential documents made their way to Moscow. But in 1951 - as the net closed in on Burgess and Maclean - they were tipped off by Philby, who had been the head of British intelligence's counter espionage unit.

The pair disappeared, surfacing five years later in Moscow.

It took years before the roles of all five were revealed and decades more for the British security services to fully recover.