Oleg Gordievsky still quite likes to play the spy. For meetings and interviews, he favours a long low hotel of roadside anonymity. He wears a black polo neck and does not smile. As he talks he leans forward, weight on the front edge of his armchair, as if ready to run for the exits. The Guildford sky darkens outside; no threat comes from the lounge of muttering businessmen. Yet Gordievsky cannot resist another gesture. For his photograph, he disappears into the gloom of the car park and fetches a raincoat. No rain has fallen for hours.

Gordievsky, who is 58, has had a life to justify such melodrama: in 1962 he joined the KGB; in 1974 he began betraying it to British intelligence; in 1985, days from detection, he defected; ever since, he has informed his way to fame as the most voluble, and perhaps the most valuable, of all double agents to work for the West. In Russia even now, Cold War fast receding, he remains under sentence of death.

Yet he does not seem genuinely anxious. "Who would take the risk of imprisonment?" he says, thin mouth turned down in disbelief, "just to kill someone with no connection to anyone in Russia any more?" These days he lets more and more people know his once-secret address; even the KGB knows - harmlessly, of course, with no "permission to liquidate". He settles back a little, warm in his armchair. "My protection was my anonymity," he says. "Now my protection is my publicity."

Last Wednesday Gordievsky felt confident enough to look foolish on live television. Previously he had taken part only in pre-recorded spy documentaries, often beneath a false beard and toupee, but this time he sat quite exposed under the lights, stout and pale and chatty as a Muscovite can be. The programme was a new Channel 4 gameshow called Wanted. Its governing idea was clever: three pairs of contestants were to play fugitives; three "trackers" were to try to catch them. Gordievsky was to anchor.

He did fairly well. He twitched for a few moments, then relaxed: his voice rolled and rasped just like a James Bond spymaster, his hands turned palm upwards and swept round in grand gesticulating circles. He enjoyed it: "In Russia such a programme would be..." Gordievsky mock-frowns, "terribly serious. Walking round with these young men and young women - I have never dreamt of being in such an environment. But it was nice."

Unfortunately, Wanted was not nice to watch. Gordievsky's fluency was as a stereotype, experience dumbed down into B-movie caricature by the crassness of his lines. And around him the programme was clanging, too: two contestants gave up and went home; the rules took half an hour to explain. This was not benign incompetence, moreover. With its gunsight motifs and appeals to the public to inform on the fugitives - scores did - Wanted was cartoon authoritarianism. And by taking part, Gordievsky, a former secret police colonel, seemed to confirm a pattern seen in his activities since defection: a steadily diminishing credibility through his association with ever more dubious causes.

Five years ago, the Guardian devoted 3,500 words to Gordievsky's "passion and suffering". As head of the KGB's London operation, he had bravely spied on his subordinates; to keep his cover, he had resisted interrogation despite truth drugs; he had fled Russia without his wife and daughters. Yet more recently he has become better known for less heroic acts. Protected and pensioned by the security services, Gordievsky has accused Western public figures of being former KGB "agents of influence" with relentless, perhaps reckless, abandon. He has also sought to impeach party leaders. In books and public statements and newspaper serialisations he has named, among others, Olaf Palme, the assassinated Swedish prime minister, Harry Hopkins, Roosevelt's closest adviser and, most notoriously, Michael Foot.

As his allegations have stacked up, and reinforced and contradicted each other, until they form a million-word hall of mirrors, Gordievsky has become known as a double agent who can't stop deceiving, a weapon of revenge for newspapers and politicians still settling Cold War scores. Last year the Sunday Times, a keen reprinter of Gordievsky's statements, paid Foot pounds 100,000 in libel damages. Gordievsky protested that the paper had "sensationalised" his information, but few doubted he was equally in the dock.

Naturally, Gordievsky sees his life as much more honourable. In 1990, he wrapped up the first of his accusations in an autobiography of more charm than its title, Next Stop Execution. He was born, he wrote, in Moscow in 1938, the son of an officer in the NKVD, predecessor to the KGB. His childhood was austere: an uncle was sent to the labour camps in Stalin's purges, then the German invasion forced the family east to a distant evacuee existence on the Chinese border. Sugar was a luxury.

After the war, the KGB offered a way out. Gordievsky's elder brother Vasilko joined in 1957; attending a special school for future diplomats, Oleg found himself drawn the same way. The appeal was not ideological: "It offered a good chance of living abroad... [and] the organisation had many glamorous and attractive features: the secrecy, the paraphernalia of espionage, the peculiar methods used..." These expectations were soon met. The KGB used dead-letter boxes and invisible ink with all the enthusiasm a young man could dream of. In 1966 Gordievsky was posted to Copenhagen.

Yet the cars and shops he found there were as dispiriting as they were thrilling: there was no "stylish modern furniture" back in Moscow. The suppression of the Prague Spring in 1968 knocked away Gordievsky's philosophical faith in Soviet communism too.

Six years of hesitation later, he met a brash British diplomat on a Copenhagen badminton court and began betraying his colleagues.

Gordievsky passed over both minutiae - everyday KGB procedures, floor plans of offices - and more strategic information - lists of agents, Russian and otherwise. Transferred back to Moscow, then to London, he learnt to conceal with ever greater facility. Informed at one meeting that "a traitor may be in the room at this moment", he pinched himself fiercely in the thigh; the pain kept his face straight.

But discovery was bound to come: the KGB had Gordievskys of their own, feeding back names as well. In 1985 he was ordered away from the Kensington stucco and lawns he so relished, back to Moscow for questioning. In the confusion of Gorbachev's dawning reforms, however, he was not immediately executed, but released under surveillance. Gordievsky already had an escape plan of Boy's Own cheek and complexity, involving a Safeway carrier bag to attract MI6, a long wait in a border forest, and a judder into Finland in the boot of a British car. It worked.

Until 1990, he lived a solitary defector's life, interminably briefing and being debriefed, husbanding his pounds 20,000 a year from MI6, watching the birds come and go in his government-funded garden.Yet Gordievsky had also abandoned and deceived his family: when they finally arrived, his wife left him. He was a sad Kim Philby in the making.

Then he lunged for "publicity". His KGB career, he realised, could bring this Western treat as it had brought all the others. First he tried a respectable route, collaborating with a Cambridge history don on KGB: The Inside Story, a thick monograph leavened with his first public naming of names. Immediately he was confronted: one American reviewer, appalled by the allegations against Harry Hopkins, called the book "squalid". Gor- dievsky says he was taken aback: "They were attacking me for being a messenger." He puts his hands on his head, miming horror. "There was so much hatred and bitterness."

The opposing opinions of Gordievsky crystallised with his first book. To the intelligence services and right-wing journalists, such as Alasdair Palmer - who with Gordievsky's help "exposed" Richard Gott, then literary editor of the Guardian, for having lunches with the KGB - he is "pretty reliable" and "morally motivated". To critics of this Conservative establishment, Gordievsky is at best unreliable - "All defectors exaggerate, and all agencies to whom defectors come exaggerate," says Phillip Knightley, an espionage journalist - and at worst a malicious opportunist.

But why should allegations from a professional double agent be believed? He answers in an impatient paragraph: "In Soviet society everyone was lying all the time, because it was totalitarian... But there's an elementary conscience inside yourself, and when you throw off the burden of lies you just return to your normal nature..."

Such certainty could justify almost anything. Historians see less consistency. Dr Sheila Kerr of Salford University teaches from his KGB book, but with a caveat: "There are two contradictory propositions in it. One, that the KGB is omniscient. Two, that they are paranoid and useless." This elasticity may be of more use to newspapers with preconceptions to support than serious scholars.

And all this has left him with serious enemies. As Knightley puts it, "I don't think he should go on holiday to Moscow."

Then again, Gordievsky does not want to. After the interview, he directs us round Guildford's one-way system with possessive care. He loves the houses with their own gardens, the climate - "the trees are still very green" - and all the official English virtues of tolerance and civility. He has a new partner, a matron at a Home Counties fortress called Wellington College. He cycles in the damp hills. Probably enough, in all, to do whatever's necessary.