My friend the spy-catcher

Christopher Andrew, although a member of the Social Democrat Party at the time, gave me a packet of toffees to distribute along the Labour front bench during the longeurs of what I anticipated would be the year's most boring parliamentary debate. Fortunately, I decided to anticipate my colleagues' pleasure on the way to the House of Commons. As I unwrapped the paper, the device inside gave out a high pitched giggle. The sweets had been bought at the London joke shop from which Andrew obtained the severed hand that crawled across his dining table.

Yet Professor Christopher Andrew, Fellow of Corpus Christi College, Cambridge, is a profoundly serious scholar. Indeed, he is the acknowledged expert on the workings of the security services in Britain, the United States and what was the Soviet Union. By co-authoring The Mitrokhin Archives - in fact doing almost all the work on the KGB files which Vasili Mitrokhin provided - he can take credit for the historical scoop of the decade. He has become one of the few academics to have made an immediate impact on public policy. If, as we must profoundly hope, the security services are forced to become more accountable to parliament, it will be the result of Professor Andrew's decision to reveal their secrets.

Inevitably, the question arises how this essentially Cambridge figure gained access to what, a decade ago, Soviet Intelligence would have gladly murdered to keep secret. There will even be suggestions that, despite the apparent embarrassment to MI5, it is the security services themselves which arranged for the KGB records to be published at this time. Nothing is regarded as too Byzantine for MI5. And cynics will point to 1990, when Christopher Andrew supported the government's insistence that Rudolf Hess had died in Spandau - despite letters suggesting that it was a double of Hitler's deputy who had been imprisoned by the Allies and that the real war criminal had been spirited off to South America.

It is never possible to completely rule out an intelligence connection. The Secret Service keeps its members' names secret. But I have always believed that Andrew (a 58-year-old Anthony Perkins look-alike) is far too independent minded either to accept the disciplines of MI5 employment or to be regarded as sufficiently discreet to join their Trappist community.

The Mitrokhin Archives is the product of assiduous scholarship. Andrew has been writing about the secret services for more than 20 years. He simply knows more about what went on inside the Lubianka than any other academic - perhaps more than most members of the Secret Service. Nobody has ever suggested that the pharaohs tipped off Howard Carter about the location of Tutankhamen's tomb. The discovery was the result of conscientious and continuous research. Christopher Andrew is entitled to claim the same.

Twelve years ago he wrote the definitive study of the British Secret Service - one of those huge, expensive books which turned out to be a good read but looked far too formidable for most people to open. He had already established an extraordinary range of connections among the intelligence community and attracted the suspicion of other academics. The Cambridge connection naturally fuelled the rumours. As Andrew said, that university "recruited far more members for the KGB than for the CIA" and we'll never know how many MI6 agents and MI5 counter-espionage officers honed their minds in its colleges. It is an easy, if weak-minded, assumption that anyone who is fascinated by spooks must be a spook himself. And it is impossible to prove the negative.

His academic detractors have never seriously questioned his integrity or doubted his scholarship. Their criticism - based on envy as much as scholarly reticence - has always been that he chose to study espionage because it was more likely to produce radio and television invitations than Andrew's original speciality, the history of modern France. There is no doubt that he enjoys performing. But he is, above all, a scholar and found a huge gap in the study of contemporary history which he was sensible enough to fill. He also has the sort of mind which is attracted by the convolutions of the security services. By comparison with the problem of unravelling the history of espionage and counter-espionage, understanding the Schleswig-Holstein question is child's play.

Andrew treats the constant absurdities of the security business with an amused contempt that serious agents would undoubtedly find offensive. If the derision is no more than his cover, the act is performed with stupendous plausibility. He discovered - to his delight - that immediately before the First Word War, when Britain was anxious to obtain information about the German battleship programme, the Foreign Office was told that the best way to make invisible ink was to mix together soot and human semen. They decided that it was a formula which one gentleman could not recommend to another.

Andrew tells with joy stories about Captain Sir Mansfield Cumming, the first head of MI6 - a hands-on operator who used to test the likely success of disguises by walking the streets of London dressed as a Chinese Kooli, a Lascar seaman or a French onion seller. During the debate on the Bill which replaced the Official Secrets Act with only slightly less repressive restrictions, I was challenged to give an example of information which had been unreasonably withheld from the public. Thanks to Andrew, I was able to reveal that when Mansfield Cumming's descendants took up amateur dramatics they asked the Home Office (for reasons of pure sentiment) which theatrical costumier their forebear had patronised. They were informed that the information was classified. When challenged on the subject, John Patten, then Minister of State, was outraged that he should be "asked to comment on individual security questions".

I have not seen Andrew since The Mitrokhin Archives made headlines. Last time we met he told me that he was about to publish a new book but refused to reveal even its title - the result, I suspect, of anxiety about selling the serial rights rather than fear that he would be arrested or assassinated with a poison-tipped umbrella. I heard him, on radio, last Monday simultaneously condemning Stalin's Soviet Union as one of the worst tyrannies of the 20th century and suggesting that Melita Norwood, the spy he had unmasked, might have been initially motivated by false hopes about a better society. It was a compassion that convinced me of his detachment. Good men make bad spies.