This will be remembered as the year we didn't find any weapons of mass destruction, but for Britain, another, more important, war had already been lost - that of our health. We have now successfully bred a generation of young people who are officially the most unfit in Europe - obese, drinking out of control, sampling drugs and indulging in unprotected sex on a massive scale. Many of them will die younger than their parents - of heart and lung disease or other chronic ailments related to the muck they are shovelling down their throats at every opportunity. A third of all our 16- to 24-year-olds are overweight, and face mental illness and a decreasing life expectancy.

This will be remembered as the year we didn't find any weapons of mass destruction, but for Britain, another, more important, war had already been lost - that of our health. We have now successfully bred a generation of young people who are officially the most unfit in Europe - obese, drinking out of control, sampling drugs and indulging in unprotected sex on a massive scale. Many of them will die younger than their parents - of heart and lung disease or other chronic ailments related to the muck they are shovelling down their throats at every opportunity. A third of all our 16- to 24-year-olds are overweight, and face mental illness and a decreasing life expectancy.

According to one consultant in adolescent medicine, the next generation will be the most infertile and obese, with the worst mental health, in the history of mankind. Another consultant said that the lack of resources and strategy for dealing with this disaster was a "scandal". The Government has cynically contemplated giving 16-year-olds the vote while demonstrating no real interest in their total well-being. Tony Blair did not start pontifi- cating about "unfit Britain" until one of his Big Conversations, in November.

There is talk of removing sweet- and drink-vending machines from schools and imposing a tougher code on television advertising aimed at the young. With all due respect, you could sum up the predicted net result of these two measures as bugger-all.

Next month the Government's Health Select Committee is expected to produce its eagerly awaited report on the state on the nation's health. It has heard evidence from food manufacturers, fast-food chains, supermarkets and advertising agencies which, not surprisingly, all claim that the situation is not their fault. The Government must be single-minded about the fight ahead. For the food lobby is far more powerful than the tobacco lobby ever was, and will use every weapon it can lay its hands on to defend its massive profits. Food is a political issue, for it is only the middle classes who can afford to eat organic food, educate their children to eat vegetables and who have enough time to shop carefully, cook food that is not prepared and have regular meal times. Cheap convenience food is as potent as drugs, make no mistake. It is confusingly labelled and packed with additives, salt and sugar. Middle-class parents do not want to have fat children. They spend time and energy ensuring that their kids take some exercise, and they ration their sugary treats. Busy single mothers and large families where both parents work often do not eat meals together; at the end of a day when the adults may have spent hours travelling to low-paid work on poor public transport there is neither the energy nor the knowledge to construct healthy home-cooked food. The attitude to food is completely different: it's not about nutrition, but about convenience and cost.

It is these people that the food lobby, with all its might, targets. And surveys have shown beyond doubt that television advertising aimed at young people works. They remember it, and start buying the junk that it so wittily and entertainingly puts before them. So when Tesco tells the Health Select Committee that it has no intention of helping parents by removing sweets from their prime position by the checkout tills, you have an idea of what is to come. Tesco has a duty to its shareholders, but as I have written before, it is totally uninterested in any real investment in its customers. The supermarket industry, like its counterparts who make cigarettes, is expert in its misuse of the English language, bandying about words such as "value" and "loyalty" when the only people profiting are shareholders.

Has Blair the courage to stand up to these powerful businessmen? Can he not see that all the money in the world poured into the NHS might as well be burnt if we are to lie around and let our young people face a future of illness and early death? Let's set aside concerns about being a "nanny" state. The situation is simply too serious. First, school meals need to be imaginative and nourishing. The utter crap served at breakfast clubs to the poorest children is an insult, packed with salt and fat. And please don't appoint a school-meal tsar, Prime Minister: we have already seen what little impact your sticking-plaster appointment of Loyd Grossman has had on hospital food.

Is there not a role for your former health secretary Alan Milburn, a father and a sensible person who has talked of the need to introduce legal limits on fat, sugar and salt in children's foods? Milburn is currently a man without a cause and would be well equipped to revolutionise the nation's eating habits. There must be money to improve school meals, laws to enforce clearer labelling and strict controls on the contents of certain foods aimed at children. Add a tax on all junk food - how about 2p a burger into a fund to improve school meals? - and ban television advertising for food and drink before 9pm, and we'd get somewhere. Stop schools selling off any more playing fields to developers and insist that no new supermarkets be built without donating land and equipment for exercise to the local community. Ban the use of famous sports people in food advertising, and use the Lottery to give every school in the country the sports equipment and staff they so desperately need. Why are these things so difficult, so controversial?

Making people healthy needs to be done in a clever, non-patronising way. It's not good enough to say that the young won't be dictated to. We owe it to them to help them to live long and happy lives. That is a worthy goal for any politician.

An outsize problem

I'm writing this in New York, where the lower floors of Bloomingdale's have been turned into a zone for those unfortunate enough to be sizes 16-24. God forbid these rails should sit anywhere near the designer Sex and the City clothing that would barely cover an eight-year-old. Next to the larger sizes is Forty Carrots café, where a homely, size-20 matron is launching into a large dish of "healthy" frozen yoghurt topped with whipped cream and walnut.

At a party I meet Debbie Harry. She has lost at least 20lb since I saw her two years ago. Is it yoga, liposuction or dieting? I dare not ask. The streets of Manhattan are divided into two camps - the X-ray thinnies, clad in floor-length mink, with tiny dogs and blonde hair, and the lumbering fatties, heading for Wolfe's deli and the pastrami on rye that would feed a family of four.

I sit in the Lever House restaurant, a fashionable place full of men in suits eating large steaks and piles of fries, and all heads turn. A girl who can't be any older than 12 stands with her mother at the entrance, wearing pink frills that just skirt her bottom. And we wonder about the rise in child pornography. If I had a child, I would care passionately what they ate and what they wore, and Coca-Cola would be banned, simple as that.