An obesity crisis with devastating implications for the nation's health will afflict nearly a third of the population within four years, the Government will say this week.
A forecast to be published by the Department of Health says that by 2010 more than 14 million people, from toddlers to the elderly, will be dangerously overweight.
The report, which will alarm health professionals and MPs, is expected to say the trend is largely a consequences of people eating junk food and of leading a sedentary lifestyle.
The acceleration in the incidence of obesity will lead to many thousands more people suffering from diseases such as heart disease, cancer and diabetes.
Sources close to the Department of Health say the figures are "stark" and "a warning to us all". Health officials are putting in place an urgent plan to halt the march of obesity and will urge adults to take "personal responsibility" for their weight. Doctors will be urged to ensure that fat patients cut their weight.
Since 2003, obesity will have risen by around 38 per cent in adults. By 2010, 22 per cent of girls and 19 per cent of boys between the ages of two and 15 will be chronically overweight.
The forecast means the Government is likely to miss its target to halt the rise of obesity in under-11s by 2010 without drastic action.
The report shows there will be a massive increase in obesity among girls under 11. The projected rise in female childhood obesity by 35 per cent has potentially devastating implications for the life expectancy of youngsters and points to a dramatic increase in health problems among women.
The figures show that there will be 1.7 million obese children by 2010 and almost 13 million obese adults. The Government is urging people with a weight problem to take action now to reduce their girth, including getting off the bus early, using the stairs and eating less junk food. Obesity costs the NHS £1bn a year and the nation £7bn a year, according to the latest figures. A Department spokesman said people worried about their weight should look at food labels and eat more fresh produce.
"Tackling obesity is a government-wide priority. But every individual has responsibility for their own health," said the spokesman. "There are simple changes people can make that will have a direct impact on their health.
"Our public health agenda is the first concerted attempt to seriously tackle rising levels of obesity. Huge progress has been made already in starting to change attitudes through the Five-A-Day campaign, the school fruit scheme, and more investment in school food."
The figures are expected to show that girls are becoming obese at a much faster rate than boys, while boys in working-class homes are putting on weight more rapidly than those from middle-class households.
In 2003, 747,000 boys and 676,000 girls aged between two and 15 were obese. Among obese boys, a higher number lived in middle-class households than in manual households. However, by 2010 the trend will be reversed. An estimated 462,000 boys in working-class households and 345,000 boys in middle-class households will be classified as obese.