Inquiries ordered by Jack Straw, the Home Secretary, and by the Commons Intelligence and Security Committee could lead to disciplinary action against high-ranking officials in the security services over their alleged mishandling of the KGB archives smuggled out by the defector Vasili Mitrokhin.
A late Labour MP, Raymond Fletcher, and former Scotland Yard detective John Symonds were named in the archives as fellow Soviet agents of Melita Norwood, and 12 more alleged spies are due to be named by the end of the week.
There were also accusations of serious blunders by the security services who dismissed Symonds' offer to give full details of his involvement with the KGB. Critics say this meant an invaluable opportunity to gain information was thrown away.
Further pressure on the security services came with claims by David Shayler, the renegade former intelligence officer, of other mistakes by MI5 and threats to name more alleged spies. He said from his home in France that he was aware of two other cases where those guilty of passing secrets had been allowed to go free by the authorities.
"I received this information while I was in MI5 from a well-respected officer who had seen the file in question. I can reveal that one these traitors was a prominent trade union leader. The union official was not tried for his betrayal of some of this country's most sensitive defence secrets and Parliament was not told," he said.
Mr Shayler said that in a separate case, a crown servant admitted passing secrets to an Eastern bloc country. As the individual was not read their rights when interviewed by their bosses and MI5, the prosecution could not go ahead.
Although details of agents such as Melita Norwood were known in early 1993 no politician was told until earlier this year. The advice of the Attorney General at the time, John Morris, was sought only when the contents of files brought out of Russia by Mitrokhin in 1992 were about to be published.
A spokesman for the government law officers' department said last night that formal consent for a prosecution of Mrs Norwood had never been sought. MI5 merely asked for advice on whether it would be sensible to prosecute the 87-year-old former spy who retired 28 years ago. Mr Morris replied that it would not.
Conservative politicians demanded a full statement and explanation last night. Tom King, the chairman of the Commons Intelligence and Security Committee, is launching an inquiry into the Mitrokhin revelations. He said it was "incredible" that Michael Howard, who was Home Secretary when Mr Mitrokhin defected in late 1992, had not been told about the contents of the archive.
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