The man investigating the defection of two of the notorious "Cambridge spies" was unwittingly confiding in members of the same group of Soviet double agents, newly released records reveal.

The diaries of Guy Liddell, deputy director-general of MI5, describe the defection of Guy Burgess and Donald Maclean to the Soviet Union in May 1951.

The diaries show that, as he gathered information on the pair, Liddell, above, was sharing it with Kim Philby, who worked for MI6, and Anthony Blunt.

In the diaries Liddell declares confidence in Blunt – but he and Philby were Soviet agents.