LOOK AT THE man sitting next to you on the Tube: his body spills on to your seat and his flabby jowls shake as he chomps noisily through his burger. Study the woman queueing with her children at the ice-cream van: their arms look like hams, their tummies like small barrels, as they gorge on the multicoloured swirls.

Look, too, at the families sitting in front of their television set: a ready-made meal balances on their lap, a tin of Coke sits at their feet, and parents and children both look like squashed accordions of fleshy folds.

Welcome to fat Britain, where one in three adults is overweight or obese, and where childhood obesity has increased threefold in 20 years. England has the fastest increasing weight problem in Europe, and comes third only to America and Australia in the developed world in terms of the percentage of the population that ranks as overweight. The nation’s expanding waistline is not only unsightly but it is unhealthy, and uneconomical.

Fat-related illnesses and diseases cost the NHS £7.4 billion a year. Here, then, is something for our politicians to sink their teeth into. Poll after poll shows that the NHS remains a crucial concern for the public. Fat should become an election issue and the party that pledges to introduce a fat tax will win huge approval ratings — it will be seen as daring to take on, Jamie Oliver-style, the giants of the food industry and the pushers of fast food.

Over the past few years politicians have tiptoed around the fat tax: it was, everyone agreed, unpopular and unworkable. But we heard this defeatist talk about school dinners, too. We were told that any change in menus would run into formidable opposition: parents wouldn’t stand for it, the dinner ladies wouldn’t cope, the pupils would rebel. Yet, one television series later, school dinners look set to be revolutionised. Impose a fat tax and the same can be true of Britons ’ eating habits outside the school walls.

Far from being a crackpot notion that could be implemented only in a Scandinavian nation the size of a pocket handkerchief, the fat tax is already in place in some parts of the United States, where the US Surgeon-General declared obesity an epidemic back in 2001. Nineteen states, including New York and California, already levy special taxes on snack foods, sweets and soft drinks. It’s a recent scheme, so the jury is still out as to its impact on the nation’s health (and weight); but, according to The Economist’s 2003 food survey, the scheme has proved eminently workable, and is already generating healthy revenues.

In Britain, the Wanless report last year ranked obesity, along with smoking and alcohol, as a major cause of preventable chronic illness, but stopped short of recommending any kind of regulation of the food industry. Wanless, like new Labour, was wary of giving rise to a libertarian chorus decrying the nanny State. Indeed, when the tax was last mooted, in 2003, by the Prime Minister’s Strategy Unit, the Food and Drink Federation immediately condemned it as unacceptable and unworkable interventionism. Yet to change the lifestyle of a nation (or a third of the nation, in this case) we cannot rely simply on government advertising or more television programmes starring cheeky chefs.

The Government’s decision to wage war on drink-driving and smoking immediately resulted in a punitive tax on these goods. A nation that can accept to pay a few pennies more for its drink and its fags will not balk at paying extra for its Twix. This is all the more so when we learn of the benefits of a reduction in fat consumption: according to the Wanless report, the nation can save £30 billion by 2022-23 if we reduce the incidence of fat-related diseases. Meanwhile, Oliver’s shock tactics showed how a ban on junk food affected children’s attention span, mood swings and hyperactivity.

The campaign for a fat tax has long been caricatured as promoting body fascism or Soviet-style interventionism. It is neither; it is a campaign against injustice. Obesity overwhelmingly affects the poorest members of society. They are the ones who are most likely to be health illiterate; as Oliver’s School Dinners showed, there are children out there who have never seen an aubergine. They are the target market of the cheap’n ’fat food producers, who know that as long as Turkey Twizzlers cost £2.98 per kilo, only the health-conscious will buy turkey thighs at £4.98 a kilo.

A fat tax, whose revenue would be reinvested in the NHS (benefiting its predominantly low-income users), would tilt the balance in favour of fresh and unprocessed food and against tempting but nutritiously trashy morsels.

The fat tax will tackle another grave injustice. Overweight Britons, who suffer a far higher incidence of heart disease, diabetes and even cancer, occupy the beds, have the blood tests, and undergo the operations that are often denied the rest of us by a cash-strapped NHS. Why should the nation’s tubbies, who choose to snack on too many crisps and walk only a few metres a day, cheat those citizens who are the unwitting victims of their medical condition rather than its architects? So forget ASBOs, the Child Trust Fund and the NHS lifestyle gurus we were promised in the last public health White Paper. A canny politician will ditch the gimmicks and go for the hard stuff. The fat tax can take up where Oliver left off, and fight the flab fast and easily. Britain will be trimmer and healthier as a result. And the NHS may get a new lease of life.

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