On my knee is Bryson's new book, a collection of essays about America, open at his clash with an airline clerk who was foolish enough to demand photo ID. This is a recurrent theme, the confrontation between petty officialdom and Bryson the pot-bellied everyman, who says the things the rest of us never think of in time. He makes us laugh at inflexible losers like the man behind the airport desk, who has "the charm and boundless motivation you would expect to find in someone whose primary employment perk is a nylon tie". Bryson, on the other hand, is sharp and smart. You can just see him standing there, legs apart, nostrils flaring and heroic beard blowing in the wind.
Must be a stylish guy, to pick on an airline worker's naff uniform. Not like the fellow in the corner, with the ginger whiskers, thinning red hair and eyes that seem to blink nervously behind large gold-rimmed glasses. His voice is nasal and a bit whiny - and he uses it to introduce himself (you will hardly be surprised to learn) as Bill Bryson. Whoops.
OK, so it didn't happen quite like that, but Bryson can hardly complain because none of the encounters in his books are true either. "I exaggerate it for the common man," he says after the introductions. "It may not be literally what they said to me but it's exactly the way it felt. It's much more impressionistic."
The real Bill Bryson is more likely to slink from confrontation, muttering under his breath, then go home and savage the other person in print, while making himself seem funny and attractive. "That was the great thing about having a column [in the Mail on Sunday, collected for the new book Notes From A Big Country]. That sense of having a platform and being able to get revenge."
One critic described him as patronising, and as mean as mouse droppings. "Who said that?" I tell him, and the answer is unexpectedly tart. "I didn't read it. I've never heard of him."
So, gentle, wry Bill Bryson, the James Heriot of his day, has a nasty streak? "Oh yeah. I have to fight that all the time. I read Lake Wobegon and thought, 'Jeez, I wish I was nice like that.' It's something I aspire to, just like I aspire not to be a slob. But then again it helps. I couldn't write the books I do if I was as nice as Garrison Keillor."
His books have changed travel writing, not least because they sell - more than two and a half million copies in this country alone, so far. The author is always the star, a lonely traveller adrift in the world with only his wit for protection. He will also be the front man for a television show to be broadcast next year, based on his biggest seller, a tour around Britain called Notes from a Small Island that has been bought by a million people since 1995. "I am taking the piss," he says of the book. "One of the things I have to say above all about the British is that you can take the piss out of them, and they're normally very good about it. I think you're crazy as hell and eccentric, but that's all part of the charm."
Bryson was born in Des Moines, Iowa in 1951, and first came to Britain at the age of 22. It was meant to be a backpacking holiday, but he got a job in a hospital, met his future wife, Cynthia, and decided to stay. The Bournemouth Evening Echo employed him as a sub-editor, and he eventually moved to London to work for the Times and indeed the Independent. Colleagues from that time remember him as a quiet, low-key chap who did a bit of writing on the side.
Never a great fan of the capital, Bryson went freelance and moved to a village in North Yorkshire. It was a bold step, vindicated when an American publisher paid $375,000 for The Lost Continent, a retracing of childhood journeys across the US. It sold half a million here but was a flop in America. His fellow countrymen and women just don't get it - but why not? "Damn good question. It's not that Americans have no sense of humour, I hate it when somebody says that. Humour is more compartmentalised there. Everywhere else in the English speaking world people are always ready for a joke, but in the States that has stopped being a feature of everyday life. Americans need to have the opening credits of Seinfeld come up to know that this is laughter time."
The trouble with Bryson is that he finds it so easy to be funny. His clever, insightful books about language, like Mother Tongue and Made In America, just don't sell as well. "A lot of people want comic books. After a while you get a little weary just cranking out jokes."
He can't seem to resist. The new book contains some genuinely moving pieces, such as the one about his son leaving home for university, but also some lazy tosh. "My wife has just called up that dinner is on the table," runs one introductory sentence. "(I'd rather it was on plates, but there you are)."
Cynthia and their four children often appear in his writing - or rather caricature versions of them do. "They are part of my life and my personal history, but they didn't sign up for all this." That's why he invented a character called Little Jimmy, to stand for all the children. "My wife was slightly more problematic. You can't just give your wife a pseudonym and expect people not to recognise who you're talking about."
In 1995 the Brysons moved to America, a decision taken by the whole family, although "I was a good deal more passive in it. As soon as we got there I thought, 'This is a big mistake.' My wife and kids loved it. The thing about being in a new country is that every little thing is fascinating. Reading what's on the back of a box of cornflakes is exotic. Going back to America, I gave up that exoticism."
Now the family also has a flat just around the corner in South Kensington. With homes on both sides of the Atlantic he can be a permanent outsider - an American in Britain who is mobbed at book readings, but an anglicised alien in New Hampshire, where he is anonymous. "That's a really nice position to be in. When things are good you can step forward and join the celebrations: if England had by some miracle won the World Cup I would have been just as entitled as anyone else to rejoice. At the same time, if something ridiculous or embarrassing happens, you can stand back and say, 'These Brits - my God! The hooligans are nothing to do with me. The Royal Family? Not my problem.' "
We have been talking for an hour and I still hardly know who Bryson is. He hides behind funny stories, charming phrases, and the alter-ego that rambles through the books. He is always amazed that some of the people he meets on book tours feel they know him. "They can't possibly. Just as you might write that I seem like a nice chap, but I could go home and beat my wife. You can only say the same about your friends, the guys that you've been drinking with. How well can you really know anyone?"
That being the case, what is there left to do but crack gags? One last question, Mr Bryson, before we part: do you beat your wife? "Oh, hardly. Nothing that would lead to a court case. No of course I don't. I'm an absolutely darling man."