Jamie: I've been a miserable father

"I wanted to find things that are really different, pastas made out of polenta or chickpeas or chestnuts.

Poor Italians, he says, "make very quick dishes with very little and it blows your mind away. They wouldn't let me touch their grub. But that's why they've still got a very rich culture and are still cooking some recipes they were cooking 300 years ago, with only that herb, and with only red wine and not white wine.

"Generally, foreign restaurants in Italy don't survive - they are quite insular like that. But Londoners will give everything a bash - Moroccan, Thai, Japanese. That's a really admirable quality.

"In terms of medium-end and topend food, London is one of the most important cities in the world. But we still haven't mastered the cheaper end of the market - under £5 or £10.

"Wagamama has done really well because they're good, quick and they're relatively low-priced. But apart from them, there isn't much around. London still isn't very good at the everyday cheap stuff."

While Wagamama displaced Nobu this month as London's most popular place to eat, according to the Zagat Guide, Oliver's restaurant, Fifteen, didn't merit a top 10 ranking. Opening to poor reviews and complaints about high prices, Fifteen has had a difficult first four years, though the future is beginning to look brighter, with an offshoot restaurant running in Amsterdam and others planned to open next year in Cornwall and Melbourne, Australia, with a South African one also in the pipeline.

"I was warned by people in the business that it would take four years to get Fifteen right and they were spot on. We've finally sorted out the things we had problems with, especially the training of the kids. We've got counsellors involved now, and we're providing the right sort of help for them.

"It's been a really interesting and tough four years developing an idealistic idea into a working business. We're now turning over more than £5 million a year, with £450,000 going to charity, and we'll be self-sufficient by next year. I'm really proud of that."

He is proud of his latest mission too: saving America. Despite missing the family he hot-footed it to the States straight after the Italian filming, however, with the corporate fat cats of the US food industry firmly in his sights.

Fresh from forcing Tony Blair into improving the dismal state of children's school dinners, the celebrity chef is now turning his attention to the obesity epidemic across the Atlantic. Ronald McDonald must be quaking in his over-sized boots. Colonel Sanders is probably choking on his deep-fried chicken legs.

For the past three weeks, Oliver has been flying between New York and California, holding discussions with US television networks for an American version of his Channel 4 show, Jamie's School Dinners.

Spurred on by the success of his UK campaign, which cajoled the Government into spending an extra £280 million on school meals, Oliver is certain he can perform a similar feat in the land of the fat. With his sizeable fortune and lucrative contract with Sainsbury's, Oliver has no reason to countenance failure. But surely trimming the vast American waistline is a challenge too far?

"We achieved such a lot in England with the school dinners campaign.

Could we do the same in the States? Absolutely," insists Oliver. "It's such an important project. Americans are so bloody unhealthy. I saw so many fat people over there and they're dropping dead all over the f***ing place."

With so many vested interests allied against him, Oliver is busy enlisting his own set of supporters to join the cause, including Morgan Spurlock, whose damning Super Size Me documentary gave McDonald's executives a severe case of indigestion. "Even if it took two years to make a US series, I'd still do it," adds Oliver. "I'd drop everything because I'd feel it was my duty."

Forever the culinary missionary, the nation's favourite Essex boy is currently planning a follow-up documentary to the original Jamie's Kitchen, which will discover the fate of the motley collection of previous Fifteen trainees.

Also on the agenda is a one-off edition of Jamie's School Dinners, in order to "check up on the Government and make sure they are doing what they promised". All of which looks likely to keep Mrs Oliver in Kleenex for a while, though at least she can take comfort from one project that her husband has recently declined.

"Channel 4 asked me to deliver its alternative Christmas Day message this year, but I've said no," says Oliver, obviously pained at the prospect of following in the footsteps of Marge Simpson, Ali G and Sharon Osbourne.

"Even though they say it's not an insult to the Queen, I quite like the royal family. Prince Charles has been supportive of the stuff I've been doing for the past four years at Fifteen and I don't want to offend anyone. Besides, I think the British public have seen enough of me being profound this year."