Vasili Mitrokhin's records led to the spy revelations

Mr Mitrokhin was the former KGB archivist whose defection to the West in 1992 brought a rich harvest of Cold War secrets, among which was the revelation that an 87-year-old grandmother from Bexleyheath, Melita Norwood, had spied for the Soviet Union for forty years.

At the heart of the ISC inquiry was the decision - made by the security service in 1992 - not to prosecute Mrs Norwood.

That decision was taken without notifying the government's law officers, raising serious issues of accountability.

The committee tabled 40 questions, designed to establish the basis on which the Director-General of M15 takes prosecuting decisions and the procedures which should be in place for informing ministers.

Christopher Andrew: Turned archive into book

The ISC also asked a raft of questions about the handling of material from the Mitrokhin Archive.

Many MP's were astonished to learn last year that in 1996, a Cambridge academic, Professor Christopher Andrew, had been given the exclusive right to turn it into a book.

The security service - no doubt braced for criticism - raised objections to showing the committee original documents, offering instead memoranda or precis of advice given to ministers.

It took a robust intervention from the Home Office to make sure that the MP's got the access they wanted.

To a certain extent, some of the lessons of the affair have already been learned.

Jack Straw: Tighter regulations expected

Last September, in the wake of the revelations, the Home Secretary met the Director General of M15, Stephen Lander, to express his displeasure.

Mr Straw announced that existing arrangements for oversight of the security service would be tightened and that it would be required to provide an annual report on all its current spy cases.

But there seems little doubt that the ISC report - which, despite its sensitive subject matter, is expected to be published virtually in full - will lead to further changes.