Britain's Labour government was not informed of allegations in the Mitrokhin spy files until last December, when information passed to the intelligence agencies by the former KGB archivist Col Vasili Mitrokhin was about to be published, the Home Secretary, Mr Jack Straw, said yesterday.
In a sign of his anger over MI5's failure to inform him of the existence of the files, Mr Straw has ordered the Commons Intelligence and Security Committee to investigate the agency's handling of the case. New measures aimed at improving MI5's accountability, including an annual report to ministers on sensitive cases under consideration, will be implemented.
The revelation that the intelligence agency kept ministers in the dark about the files, even though one of those named - Ms Melita Norwood (87) - had been under suspicion since 1945, underpins the seriousness of questions being raised about the accountability of the intelligence community.
However, the shadow home secretary, Ms Ann Widdecombe, said Mr Straw's statement "beggars belief" and she questioned why he did not tell Parliament or the Prime Minister, Mr Tony Blair, about the file when informed of its existence nine months ago.
In a statement issued after meeting the director general of MI5, Mr Stephen Lander, Mr Straw revealed that it was not until 1996 - four years after Mitrokhin smuggled handwritten copies of KGB files out of the former Soviet Union - that the intelligence service told the then Conservative government about the files. The Conservatives took the decision that due to the "extraordinary circumstances" of the case, Mitrokhin's story should be published. Sir Malcolm Rifkind, foreign secretary in 1996, has said the decision was taken with his consent.
The Mitrokhin material was then made available to the Cambridge historian Prof Christopher Andrew, whose book, The Mitrokhin Archive, detailing the activities of KGB spies across the world and co-written with Mitrokhin, will be published this week.
After a day of questions about who knew what and when, Mr Straw said he was first informed of the allegations against Ms Norwood in December 1998. Mr Blair was not informed of the existence of the files until last week, Downing Street said.
The statement revealed that Ms Norwood had been under suspicion by the authorities since 1945 because of her communist sympathies. But while the Mitrokhin file confirmed their suspicions of her, the intelligence service considered the material "did not on its own provide evidence that could be put to a UK court", Mr Straw said.
It now seems unlikely that Ms Norwood will face criminal charges arising from her admission that she passed Britain's atomic secrets to the former Soviet Union during a 40-year career as a KGB agent.
Mr Straw said the former attorney general had ruled earlier this year that 1992 - when Mitrokhin defected and revealed the identity of several British KGB agents - was "the last opportunity" to launch a prosecution against her.
However, law officers will be studying the transcripts of a BBC documentary on the Mitrokhin files next Sunday that will include an interview with Mr John Symonds, a former Scotland Yard detective who became a KGB agent in 1972, to consider whether charges could be brought against him. The Home Secretary said he did not know about Mr Symonds's activities as a spy until last weekend.
Mr Straw's statement came as the Mitrokhin files yielded the names of two more KGB agents working in Britain, Labour MPs Mr Tom Driberg and Mr Raymond Fletcher, both now dead.
The Mitrokhin archive will also provide details of the KGB's supply of arms to the IRA in the 1970s. Details of plans to recruit agents in Northern Ireland and Scotland and a plot to disrupt the investiture of the Prince of Wales in Cardiff in 1969 will also be revealed.
A British army officer was bribed with 40 kilos of gold to hand over White Russian generals to Soviet intelligence in 1945, the London Times newspaper reports today.