But the defection was hampered by the need to bring six large trunks buried in the garden of Col Mitrokhin's dacha outside Moscow. MI6 officers, including renegade officer Richard Tomlinson, posing as workmen loaded them into a van. Mr Tomlinson was jailed two years ago after attempting to publish a book about his secret service exploits. He was released in April last year.
These trunks contained the "crown jewels", a KGB encyclopedia of their aims, tactics and agents. Thousands of files were copied from the KGB's innermost archive. The MI6 operation to lift Mitrokhin was so successful Russian intelligence did not realise the retired archivist had gone for weeks and was in Britain, telling all to MI5 and MI6.
MI5 analysts could not believe their luck when they read the files. There are 25,000 pages of material on KGB operations, a unique insight of the Soviet world spy network.
The documents reveal what targets interested the Soviet Union for the 45 years of the Cold War and expose in gory detail the seduction and blackmail of weak foreign officials by agents. Even the murders of enemy agents are discussed.
Exposure of an 87-year-old great-grandmother in Bexleyheath and a former Scotland Yard detective as KGB spies is just the beginning. The documents, now to be examined by the Commons intelligence committee, are described as the West's most complete picture of Soviet espionage.
Up to 12 more Britons recruited into the KGB will be unmasked this week. Professor Christopher Andrew said: "One will be a prominent public figure who is now dead."
Other evidence will reveal how the Soviet Union preyed on the Concorde design team and built its ill-fated Concordski imitation. The Mitrokhin archive shows an aircraft engineer codenamed Ace handed over 900,000 pages of technical data and blueprints.
The files will help to identify KGB agents in Britain still "live" up to the fall of the Berlin Wall. This involves up to 100 Britons, agents or "helpers".
There are details of the KGB's supply of arms to the IRA in the 1970s and a plot to disrupt the investiture of the Prince of Wales, codenamed Operation Edding, to be perpetrated with Welsh extremists.
The archives also show the vengefulness of the Soviet machine towards those accused of betrayals. They considered maiming the ballet stars, Rudolf Nuryev and Natalya Makarova, who defected to the West in 1961 and 1970 respectively. The plan was abandoned because the KGB feared exposure and a wave of public opprobrium.
The files also show how the KGB planned to recruit President Carter's national security advisor, Zbigniew Brzezinski and Cyrus Vance, who later became secretary of state. Both attempts failed.
The Soviets were successful in recording conversations between Henry Kissinger, at the time national security advisor to President Nixon, and diplomats, as well as his girlfriend. Listening devices were also planted inside the room used by the US Senate Foreign Relations Committee.
Spies placed in big US companies such as IBM and General electric ensured the KGB gathered secret commercial as well as defence information. The files show how Moscow regularly received plans for new tanks and aircraft.
The Soviet spying machine was so successful that nearly half of the defence development projects being undertaken in Russia were based on secrets stolen from the West.
The KGB considered sabotaging the Port of New York as well as targeting key infrastructure such as dams and electricity grids. They planted stories discrediting the integrity of the black civil rights leader Martin Luther King. And even considered causing an explosion in an Afro-American community that would have been blamed on white racists with the intention of destabilising American society.
Mrs Norwood, codenamed Hola, is believed to have recruited for the KGB. One is a civil servant codenamed Hunt. Through the 1970s he was paid for information on British weapons, and arms deals. Professor Andrew said there are many more files on the US than on Britain. "This reflects the greater number of operations the KGB undertook there," he said. The US has just declassified the Venona code files, which unmasked Soviet agents in the 1940s and 1950s. These result from the cracking of Soviet military intelligence messages to Moscow.
There are believed to be 300 Soviet spies in Britain and America not yet publicly identified. The files reveal extensive penetration of America's defence establishment. By 1975, the archive shows the KGB had 77 agents and 42 key contacts in US scientific and technical establishments, including those involved in nuclear arms.
Robert Lipka, an employee of the codebreaking National Security Agency who spied for the KGB, did immense damage to the West. He has been sentenced to 18 years, because of Mitrokhin's material.
His files also reveal KGB officers were placed as special assistants to three successive UN secretary generals.
The Traitors Who Got Away
THE PROSECUTION of Melita Norwood is not a straightforward matter. There are others who leaked information to the Soviets and have not been prosecuted.
In 1996 the release of the American "Venona" files - deciphered Soviet messages from the Second World War and early Cold War - led to the unmasking of Theodore Hall, an American scientist working on the "Manhattan Project" to create the atomic bomb.
In 1996, Hall admitted that he passed information to the Soviet Union. He has never been prosecuted and lives in retirement in Cambridge, England.
Anthony Blunt (1907-1983) was the "Fourth Man" of the Cambridge spy ring. He acted as talent-spotter, supplying the names of likely recruits to the KGB. He confessed only when promised immunity from prosecution after the defection of Kim Philby in 1963.
However, Vasili Mitrokhin's files have already resulted in successful prosecutions. Robert Lipka, who was an employee of the US's top secret National Security Agency, was arrested by the FBI. He was recently prosecuted and jailed. It is understood he confessed to passing secrets to the Soviet Union in the 1960s.