Doctors have warned that almost half of all adults in Britain will be classified as obese within the next 20 years.
They predict that on current trends an extra 11 million people will be severely overweight by 2030, bringing the total to 26 million.
Only tough government action, including a tax on unhealthy food, can slow the trend, they say.
The bleak prognosis comes in a series of expert reports commissioned by prestigious medical journal The Lancet .
The doctors have produced a league table of possible actions that could be taken to curb the epidemic.
At the top is a 10% tax on high-calorie food and drink.
Professor Klim McPherson, an epidemiologist at Oxford University, said the government needs to learn the lesson of tobacco taxation, which has dramatically reduced smoking rates.
"A tax wouldn't be unpopular if people knew what the issues are," he told Sky News.
"People know obesity is a real problem. People don't know, as individuals, what to do about it.
"Governments do know what to do about it and if they could persuade people, as they easily could, it would be a popular action."
The experts also propose restrictions on junk food advertising and initiatives to warn children not to spend too much time sitting around watching TV.
They say the initiatives are much more cost-effective than obesity operations and some fat drugs.
Tam Fry, of the National Obesity Forum, said: "Children are born thin. It's what we do to children that makes them obese.
"Adults have choice, but children can't make infomed decisions about what they're eating."
A spokesman for The Department of Health said obesity was a priority.
"We are encouraging people to make simple changes, such as eating more fruit and vegetables, cutting down on fatty foods and being more active.
"We have no current plans to impose a 'fat tax', but we are working with food companies to reduce fat, sugar and salt and ensure healthier options are available."
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