One fifth of boys will also be obese and at least one third of adults, added the report by Britain's Faculty of Public Health, the Royal College of Physicians and the Royal College of Paediatrics and Child Health.

"This report highlights the terrifying health consequences of the obesity epidemic that will particularly impact on our children," said Professor Peter Kopelman, who chaired the report.

"Storing up problems -- the medical case for a slimmer nation" called for a government task force to develop a strategy against the threat, highlighting the benefits of healthy eating and exercise.

"The UK has the lowest physical activity for school children in Europe, and the problem is worst in the most vulnerable groups who are also the most socially deprived," said Sian Griffiths, president of the Faculty of Public Health.