According to researchers over 25% of British school children are clinically obese and they lay the blame squarely on junk food and a lack of exercise.

The researchers say such factors have created a ‘public health timebomb’ .

The figures are based on data on 2,000 children and come from the National Health Survey for 2004; experts are concerned as research has shown that children who are obese between 11 and 15 are twice as likely to die in their 50s.

The official survey shows that the figures are almost double what they were ten years ago and half of teenage girls and more than a third of teenage boys in England are overweight or obese.

The researchers measured the height and weight of 11-15 year olds, and found 26.7% of girls and 24.2% of boys qualified as obese - nearly double the rate in 1995. Among children aged 2-10, 12.8% of girls and 15.9% of boys weighed above the obesity threshold - also well up on 10 years before.

A government pledge in 2004 to stem the growth in childhood obesity by 2010 has yet to be published in full and it has been revealed in a report by the National Audit Office that it has taken 31 experts as long as 18 months to decide how childhood obesity should be measured.

The initiative appears to have become bogged down in bureaucracy resulting in numerous campaigns but little money to implement them and no clear evidence of which strategies might work.

Diabetic organisations are calling for a ban on junk food advertising aimed at children and want more done to encourage people to exercise.

It is appears that 80 per cent of people with diabetes are overweight or obese at diagnosis and as obesity increases, the average age of the diagnosis of type 2 diabetes lowers.

This raises the spectre of children losing limbs and becoming blind as they grow up and develop the serious complications of the condition.

The obesity rate among adults was also found to have risen to 24%, despite people exercising more and eating more fruit and vegetables.