Blunt's memoirs revealed little new about his spying activities
The memoirs of former spy Anthony Blunt reveal how he regarded passing British secrets to Communist Russia as the "biggest mistake of my life".
He supplied hundreds of secret documents to the Soviets while a wartime agent for MI5.
Blunt was part of the infamous Cambridge spy ring, with Kim Philby, Guy Burgess and Donald Maclean.
His manuscript, at the British Library in London, says a "naive" desire to help Moscow beat fascism motivated him.
Blunt wrote the 30,000-word document after former prime minister Margaret Thatcher exposed his treachery in 1979.
The revelations had led to a man who had worked as Surveyor of the Queen's Pictures being stripped of his knighthood.
His version of events was given to the library in 1984, the year after his death, on condition that it was not displayed for 25 years.
In it, he describes his recruitment by Moscow: "I found that Cambridge had been hit by Marxism and that most of my friends among my junior contemporaries - including Guy Burgess - had either joined the Communist Party or were at least very close to it politically."
However, Burgess - who had already begun working for Stalin's Comintern - persuaded him not to join the party but instead to work undercover.
"What I did not realise at the time is that I was so naive politically that I was not justified in committing myself to any political action of this kind," says Blunt.
"The atmosphere in Cambridge was so intense, the enthusiasm for any anti-fascist activity was so great, that I made the biggest mistake of my life."
Blunt's memoirs reveal little about his espionage activities during World War II, during which he passed on top-secret material decoded from German radio traffic.
He claims he later became disillusioned with Moscow, wishing only to "return to my normal academic life".
However, he says his knowledge of the others in the ring made this impossible.
By 1951, Philby had become head of the counter Soviet section of the Secret Intelligence Service, MI6.
He warned Maclean to flee to Russia - which he did, along with Burgess - after learning he was about to be unmasked as a traitor.
Maclean's defection led to suspicion falling on Blunt, who was also advised to flee.
But Blunt wrote: "I realised quite clearly that I would take any risk in this country, rather than go to Russia."
He was eventually denounced in 1964 and confessed when offered immunity, giving the authorities "all the information that I had about the Russian activities".
He went back to work "not only relieved but confident", believing it was in the security services' own interests to keep his story quiet.
So after the "appalling shock" of his public exposure, he says he considered taking his own life.
Not wishing to upset his friends and family further, he instead sought refuge in "whisky and concentrated work" - the product of which is now on display.