Doctors' leaders today called on ministers and the food industry to take urgent action to tackle the "terrifying health consequences" of the UK's obesity epidemic.
The Royal College of Physicians, the Faculty of Public Health and the Royal College of Paediatrics and Child Health warned that if current trends continued at least a third of adults, a fifth of boys and a third of girls would be obese by 2020.
The report by the three royal colleges, Storing Up Problems: the Medical Case for a Slimmer Nation, recommends the establishment of a Cabinet taskforce to ensure that healthy living is promoted by the NHS, local authorities and schools.
It calls for the government to launch a campaign to educate the public about the benefits of healthy eating and being active.
The royal colleges said the food industry and the Food Standards Agency should improve food labelling, and work together to promote and produce healthier foods.
They said more research was needed into the causes of the rising rate of obesity to help healthcare workers prevent and treat those at risk.
The report also calls on parents not to drive their children to school, adding that town planners should do more to encourage people to drive less and walk more.
Professor Peter Kopelman, the chairman of the working party which put together the report, said: "This report highlights the terrifying health consequences of the obesity epidemic that will particularly impact on our children unless effective and coherent preventive measures are taken.
"The report identifies responsibilities of every segment of society from central government to individual families, and makes practical and realistic recommendations that need to be taken forward immediately to achieve a slimmer and healthier nation."
Obesity is estimated to lead to 30,000 deaths a year in the UK, causing health problems such as heart disease, strokes and diabetes.
More than half of the UK population is either overweight or obese. In 2002, 70% of men and 63% of women were classed as overweight or obese.
The royal colleges' report warns that the current generation of children show signs of becoming the most obese yet.
It said that the rate of obesity among children aged two to four almost doubled between 1989 and 1998, from 5% to 9%. Among those aged six to 15, the rate trebled from 5% in 1990 to 16% in 2001.
Professor Alan Craft, the president of the Royal College of Paediatrics and Child Health, said: "Obesity is a major issue for children as well as adults.
"We must find ways of tackling it in childhood if we are to prevent the major complications in adult life. Prevention is everyone's business."
Professor Sian Griffiths, the president of the Faculty of Public Health, said: "We are getting fatter because we are not taking enough physical activity and we are eating the wrong foods.
"For example, too many children are taken to school by car and too few ride their bicycles.
"Obesity is a serious threat to our wellbeing and we need to get the health balance right, not only through taking individual responsibility but through measures which make it easier to make healthier choices about how we live."
The parliamentary spending watchdog, the National Audit Office, estimates that obesity costs the NHS at least £500m a year, and the wider economy £2bn.
The health secretary, John Reid, last week launched a public consultation to improve the nation's health, which will feed into a white paper tackling problems including obesity, due to be published this summer.
He described the royal colleges' report as "a valuable contribution" to the consultation.
"The authors are right to highlight the problem of increasing obesity, particularly among our young people," he said.
"They are also right to point out that this is not simply a matter for the government, but for everyone who wants to ensure people live the long and healthy lives they deserve."
The Commons health select committee has also been investigating the UK's obesity epidemic and is due to publish its findings in the next few months.
