Food experts are calling on the Government to introduce annual weight and fitness checks for all schoolchildren to prevent an epidemic of obesity.

British nutritionists and child health experts believe that children as young as five should have their body mass index (BMI), a method of calculating weight, worked out each year in order to monitor their growth. They believe that, if parents were properly informed, they would do more to help their children shed pounds and cut the risk of developing fat-related diseases in later life.

In Boston, Massachusetts, schools have already begun to carry out compulsory weight and fitness checks, which are included in the school reports at the end of the year. Children found to be at serious risk are encouraged to enrol on exercise programmes, and advised to follow diets.

Doctors discovered that parents who received the report cards were almost twice as likely to acknowledge that their child was overweight than those who did not receive a card, according to a study published in the Archives of Pediatrics and Adolescent Medicine .

Professor Philip James, who chairs the International Obesity Taskforce, and who wrote a seminal report on diet for the World Health Organisation in 1990, said the UK should consider compulsory checks as part of its strategy.

'Having healthy school meals is fine, but the amount of food eaten in school only totals 15 to 16 per cent of a child's annual intake,' he said

'The truth is that the diet of the vast majority of British people, particularly in the poorer areas, is atrocious.'

He added: 'If we could take the evidence from American schools and apply it to a British context, it could hep us prevent overweight at a very early stage in a child's life. The older they become, the harder it is for them to lose that fat, and the more likely they are to develop diseases such as diabetes.'

Tam Fry, director of the Child Growth Foundation, also believes annual BMI checks are essential. BMI is calculated by taking someone's weight in kilograms and dividing it by their height in metres squared. A score over 25 is considered to signal overweight, while over 30 falls into the obese category.

Fry said: 'The Government is saying "We don't want to be a nanny state", but it is also the duty of the Government to oversee the health of the nation. They might think it will upset kids and their parents, but this is not about stigmatising children - it's about protecting them.'

He said parents were giving children far too much choice about their meals, when the evidence suggested that sticking to meals which offered little choice but plenty of fresh food was far better.

However, that view is not supported by everyone. Professor David Hall, past president of the Royal College of Paediatrics and Child Health, said the problem lay in the lack of evidence to show that targeting individual children would lead them to lose weight.

'There is no doubt that the rate of obesity is exploding. It's a massive problem for the whole of the Western world. But we are more likely to be successful if we bring in measures that affect the health of the whole population. It's about making it easier to walk to school, getting kids to stop watching hours of TV, offering better school food, and providing more sports facilities.'