The decision to formally inform the Queen comes amid growing concern in Whitehall that the truth will inevitably emerge following the death of Blunt, who was seriously ill with cancer. Journalists had already investigated this story, and they were no longer bound by the fear of defamation.
Blunt first came under suspicion in 1951, when fellow spies Guy Burgess and Donald McLean fled to the Soviet Union.
He had been a close friend of Burgess since their time studying together at Cambridge in the 1930s – part of the so-called Cambridge Five spy group.
During the Second World War, Blunt worked for MI5, after 1951 he was interrogated 11 times by members of the Security Service, but always denied espionage.
Then the American Michael Straight told the FBI that he was recruited by Blunt himself as a Russian agent.
