A leading doctor has accused schools of making children more overweight after government figures showed rates of obesity rise through primary school.
Dr David Haslam, clinical director of the National Obesity Forum, called for children to do more PE and be made to play outside during breaks after data showed the proportion of pupils classed as overweight rises by nearly 10% between the first and sixth year of school.
Nearly a quarter (22.9%) of four- or five-year-olds in England are deemed either obese or overweight, with the figure rising to 31.6% by the time they are aged 10 to 11, according to a health department survey. In both age groups, boys were more likely than girls to be obese.
The findings, from the National Child Measurement Programme, which weighed and measured 80% of pupils aged four to 11, will make grim reading for ministers who have pledged to tackle Britain's "obesity time bomb".
Haslam said it was a "scandal" that the rate of children who are overweight or obese rises while at school.
"For our schools to be causing our children to become overweight is pretty terrifying," Haslam said. "It shows that physical exercise has to be more of a priority at school.
"When I was at school you got kicked out at dinner time to play outside, now children are allowed to spend their breaks on computers - that needs to change."
Haslam called for legislation to force fast-food outlets and sweet shops to close at the end of the school day. "Perhaps they should be made to close for half an hour or an hour until around 4.30pm."
Although the proportion of children between four and five and 10 to 11 classed as overweight rose by 1%, the number classified as obese nearly doubled.
The situation is worst in London where 11.3% of four- to five-year-olds and 20.8% of 10- to 11-year-olds are classified as obese.
Last month, the government launched a £372m strategy aimed at cutting obesity in England. It proposed offering cash incentives to encourage obese people to lose weight and suggests schools monitor lunchboxes to ensure children are eating healthily.
A health department spokesman said: "There is a particular focus on children, with an aim to reduce the proportion of those who are overweight and obese back to 2000 levels by 2020."
Kevin Brennan, the children's minister, said 86% of children now enjoyed at least two hours of PE and sport each week.
"We now have plans to increase this to five hours each week by 2011," he said.
