The Mitrokhin archive was first revealed in 1992 - why were the spies not prosecuted then?

Although the archive was revealed in 1992, it took two years to establish that the spy codenamed "Hola " was Melita Norwood, living in Bexley Heath.

We know from the Home Secretary's statement on Monday that in the Attorney-General's view, it was too late after 1992 to mount a successful prosecution.

We don't know on what grounds he gave that opinion -but it was probably a ) that there was insufficient evidence admissible in an English court and b ) public interest - chiefly the age of Mrs Norwood and the fact that most of the damage she had done was in the 1940's.

Is it likely any of the spies will be prosecuted now? Who decides? Is the age of suspects important?

It is most unlikely that the spies we know about will be prosecuted. However, there are more disclosures to come and it can't be ruled out that there may be a sound case for prosecuting one or more.

The decision on a prosecution would be for MI5 on the advice of the Attorney- General.

The age of a suspect would clearly be a significant factor on "public interest" grounds but far more important would be the availability of credible evidence and witnesses.

Why are there no prosecutions when former spies like David Shayler are living in exile?

I think the answer is the end of the Cold War. If we still regarded Russia as our mortal enemy trying to subvert the West, prosecutions might be considered, even after such a time lapse.

Whereas, ex-agents like Shayler ARE considered a threat precisely because they have much more contemporary knowledge.

When did the current Home Secretary first find out about the Mitrokhin archive?

Mr Straw says he was "made aware in general terms" in 1997.

Who else knew? What about former home secretaries?

At the time that Straw first knew of the Mitrokhin material, it appears that only Malcolm Rifkind, the Conservative Foreign Secretary knew. He gave his authorisation in 1996 for the Mitrokhin material to be published. Michael Howard says he didn't know as Home Secretary.

The Home Secretary has announced an investigation of MI5 - why?

Straw is clearly angry that MI5 decided not to tell ministers about the Mitrokhin material for five years. He feels that under accountability guidelines, MI5 should have been much more forthcoming.

How much power does Jack Straw have?

Straw is responsible to parliament for the performance of the security service. If there is a spy scandal he is the one ultimately answerable.

Is this type of spying still prevalent?

Spying these days tends to be more industrial than political but most countries - not just Russia - maintain intelligence services who rely on the services of spies.