He's happy, in love with a younger man and cunning enough to have gone on holiday to Belgium instead of killing himself. "I'm unquestionably a fox," says Stephen Fry

Stephen Fry is demonstrating the Smyslov Screw on a table at London's Groucho Club. "It's like this," he says, indicating the chess trick by twisting his lighter down so hard that our cappuccinos spill over. "Oh, I'm so terribly sorry," he adds, thoroughly mortified, reaching for a napkin and upsetting the table again. His latest novel, The Stars' Tennis Balls - the story of public school boy Ned Maddstone's betrayal at the hands of his fellow pupils, his years spent as a political prisoner and his eventual, gruesome revenge - features the Screw as a ploy designed to unnerve one's opponents. Today, however, it just serves to make the 43-year-old comedian, actor and novelist even more endearing.

With three novels and an autobiography, cameos in Blackadder and roles including Peter in Peter's Friends, Wilde in Wilde, Jeeves in television's Jeeves And Wooster and, er, Fry in A Bit Of Fry And Laurie, Stephen Fry is as respected for his talents and intellect as he is loved for his quintessentially British demeanour. He is also the narrator of the Harry Potter audio books and is currently being mooted as the next Doctor Who.

His relationship with fame is fraught, nonetheless. He once famously said that the British public regards him as a sort of public kitten, a cross between Alan Bennett and the Queen Mother. Sometimes, he says in his plummy Oxbridge vowels, it's as peculiar to be told you're loved than you're not, especially when people don't even know you.

"But there's times when you read about yourself in a newspaper and get the impression that the whole country thinks you're some ghastly poof who should be put down," he muses, lighting the first of innumerable Marlboro Reds. "Then you might be in a shop and someone will come up and say something very sweet, so you know not everyone thinks that."

For somebody who's been called "the most brilliant man in Britain", it's surprising to discover that Fry still frets over the approbation he both craves and rejects. Interviews over the last few years have trumpeted that he is happier now than he ever was. Or rather, that he is happy now, when he wasn't at all before. This is exemplified by the fact that he divides his life into two neat eras, BB and AB, or Before and After he went AWOL in Belgium.

His disappearance was sparked by hostile reviews of his role in the 1995 West End play, Cell Mates, but they were really the last straw in a litany of insecurities stretching back to his childhood. The gifted but miserable middle child of a "cold hearted" physicist, Fry's earlier years were beset by geeky self-consciousness and a loneliness that neither his fame nor his furious work ethic assuaged. He went to Belgium, the first place the ferry was heading, in a desperate attempt to leave it all behind. It was that or topping himself, he says. He'd actually driven to a quiet spot, intending to stop up gaps with a duvet before succumbing to exhaust fumes, before he realised that Belgium would be infinitely less upsetting for all concerned.

After a public appeal he returned to London (he also owns an old rectory near his mother's house in Norfolk), where he was prescribed lithium for manic depression. He then headed off to live, more or less anonymously, in California for a year, before coming back to Old Blighty. "I realised I couldn't run away from myself," he says sagely. He vowed that he would never again: a) work so hard, b) read his own reviews, c) feel so irrationally obliged to strangers.

Today he's not doing so well on that last point. "Will you have another coffee? A cigarette? Something to eat?" he enquires, in between questioning me about my life, laughing heartily at my jokes and locating my next appointment for me in the A-Z.

There's a genteel nerviness about this big, bendy-nosed bloke in the Norwich City football shirt, slacks and comfy brown brogues. (Although, having lost a couple of stone after a diet recommended to him by Julie Andrews, he's not as big as he was). Despite the fact that the Groucho staff obviously love him, that various club members stop to chat - Clive James, revealed suddenly and surreally by a sliding partition, waves cheerfully - Fry is still uncommonly keen to be liked.

Part of this, perhaps, is to compensate for being in possession of a brain that works at double the speed of everyone else's, as the plot twists, witticisms, references and craftsmanship of The Stars' Tennis Balls illustrate. Just give him a topic and watch him go.

As we segue from his friend Prince Charles ("When I stay at Buckingham Palace I always call my mother on the mobile and go, 'Guess where I am?"') to GM foods ("No slithering creatures are going to come and bite our arses off") and his affiliation with the Blair Government ("But I don't agree with their negative stand on immigration and drugs"), he barely draws breath. Add this to his penchant for self criticism, being Stephen Fry must be exhausting work. His pal Emma Thompson once gave him a fishing rod, in the hope that the pastime might chill him out a bit.

"At the risk of sounding pretentious," Fry says, his heavy-lidded eyes twinkling, "there's that beautiful essay by Isaiah Berlin on people being either hedgehogs or foxes. Hedgehogs are sort of cute and deliberate and know one thing very well. A fox is quick and sharp and restless and stealing things. I'm unquestionably a fox, which is sometimes a more tiring thing to be."

So does he still feel compelled to be all things to all people? "Foxes are masters of disguise. I do have different circles of friends. I can play snooker here with the lads and go to football matches" - he fingers the little canary logo on his shirt - "or I can be with my gay friends who collect pictures and talk about 'Piranesi, my dear'. I have a terrible time giving dinner parties because my boyfriend wants to invite all of them, but I can't do that."

There it is, the B-word. The word for which BB and AB should really stand. For nigh on 15 years Fry proclaimed himself celibate, speaking of his loathing for relationships and sex. "I think I said something about 'damp tufted areas interacting'," he mutters shamefacedly, and we roll about laughing. Although he "threw" himself on biographies of Somerset Maugham, Harold Acton and Oscar Wilde, he sublimated his early homosexual feelings and - whether linked or not - embarked on a bit of fox-like kleptomania. After a stint in Somerset's Pucklechurch Remand Centre he got his act together sufficiently to be accepted by Cambridge, but has never been romantically linked with anyone. Until now.

As genuinely friendly as Fry is - and he is, indeed, a remarkably likeable chameleon - he steadfastly refuses to discuss his partner, save for the fact they were introduced in 1996, that he is ten years younger and not in show business. "Sorry," he says, looking it. "I don't talk about him." Still, his delight in his newfound coupledom is obvious. References to "my chum/partner/boy-friend" pepper our conversation; he admits he derives as much pleasure from having someone to worry about as he does from having someone, period.

"For two and a half months I'd get up at 3.30am, and go to bed at five or 6pm," he says, when asked about writing The Stars' Tennis Balls. "That was all work, apart from occasionally flouncing into the kitchen and making myself some coffee. It was like a drug-induced state. My poor partner would say something to me and I'd go, 'Mmm? Mmm'. He knew I wasn't listening to a single word." Fry beams happily.

On a bus about a year ago, Fry noticed a group of floppy-haired public school boys sitting up the back, talking in their loud, privileged voices. A dark -haired boy of the same age sat a few rows in front. "I thought, 'What does he think of them? Is it contempt? Or does he want to be one of them?' Then I thought about the arrogance of the public school manner that can be like a dagger in the heart." Fans of Fry's previous literary endeavours may be taken aback by Ned Maddstone's bloodthirsty vendetta after 20 years inside. "It is bleaker than my other books, although it has the quality of an adventure story. What also interested me was starting off with a character who is likeable, and who has good cause for revenge. And of course revenge is probably one of the oldest stories that exists, Hamlet being the obvious example."

Revenge is a dish best served hot, he believes. "Ned was a terribly innocent chap who was seriously done down, so is therefore the person you follow and sympathise with as you read. Then at some point you think, 'Hello, he's going too far, has he gone mad?' Part of us wants him to do this, but when he does you feel slightly sick. It's like when you see footage of concentration camps and want to get those guards' heads and grind them into a wall. But when you see footage of a 90-year-old Ukranian war criminal shuffling down the street, it's too late ..."

So how vengeful is Stephen Fry? Did he ever lie awake at night conjuring elaborate punishments for the critics who dissed him? "Ha ha," he laughs, and you imagine that he probably did. "No," he insists, "I'm not like that in the least. Of course, like everyone I have my moments. If you go to your car" - Fry drives an old black London cab - "and find the window smashed and the tape player missing, for five minutes or so one pictures slamming someone's face against the bonnet and saying, 'You bastard!' But it goes very quickly."

Once Fry had decided on the story, he invented a title ("We are merely the stars' tennis balls, struck and bandied which way please them," wrote Webster in The Duchess of Malfi) and drew up a rough plan. He was drifting off to sleep one night when he got the awful feeling it had all been done before. "It was so different in milieu that it took me ages to think. Then I got up, went downstairs and put on my video of The Count Of Monte Christo, which is one of those classics everybody's heard of but seldom read." And there it was. "So I decided to do a reworking of the story, and I've put in 15 or so cunning references which readers should find for themselves." There'll be a competition on his website, he says, so he can't be giving the game away.

Ever the polymath, Fry is off to Jerusalem to film The Discovery Of Heaven, a "sort of cross between Jules et Jim and Indiana Jones" in which he rather fittingly plays a philologist. He has recently completed the screenplay for Evelyn Waugh's Vile Bodies, which he'll be directing in the new year. As for the good Doctor, "Everything to do with Doctor Who is labelled 'top secret'. But at the risk of sounding pompous, if the scripts were good ..." He pauses, puffs on his fag and qualifies himself. "Of course," he says with characteristic, frustrating modesty, "there are plenty of other people who would do it better."

He'll be taking his chess board with him to Jerusalem. As with Ned in The Stars' Tennis Balls, the game helps to clear his mind, if not calm him down. "It's not about anything in the real world. Just 64 squares and silly little symbols that move around. A complete closed system." In his first year at Cambridge he shared a room with a chess master who could play several boards at once. Blindfolded. "I think everybody has a much greater capacity for thought than one believes. We only use about 20 per cent of our brain cells, you know," says Fry, who engages a far greater percentage than most.

And if logic lucks out, try the Smyslov Screw, right? "Right!" Fry bumps the table with his knees. "Oh, I've done it again!" he wails, before shaking off his embarrassment with a laugh. "Now, now, Stephen," he adds fondly, ''do behave yourself."