Nearly half of the children in England and Wales have unhealthy diets, dominated by calorie-laden snacks such as crisps, fizzy drinks and sweets, a TES survey reveals today.

A strong link between social class and healthy eating is also disclosed by the poll of more than 700 parents. Youngsters from the poorest backgrounds are more than twice as likely as middle-class peers to eat mainly junk food, the survey found.

Parents also reveal that their children can spend twice as much time playing computer games or watching television as they do in active play.

Professor Neil Armstrong, director of the children’s health and exercise research centre at Exeter university, said the findings confirmed the need to tackle Britain’s child obesity “crisis”. Writing in today’s TES he warns: “The prevalence of obesity is now three times greater than it was 20 years ago. It appears to be increasing more rapidly in England than anywhere else in Europe.”

The survey suggests that headteachers are not doing as much as they could to combat the problem. Nearly eight out of 10 parents want a ban on school vending machines, which exist in about 95 per cent of secondary schools.

Today, The TES launches a campaign, “Get Active”, designed to help schools to tackle the worrying trend of childhood obesity.

Bob Doe, editor of The TES, said: “Our campaign is not about shaming schools into doing something about the ills of an increasingly sedentary society. It is to support those who see teaching about more healthy lifestyles as an essential part of learning for life.”

Professor Armstrong urges all schools to develop their own physical activity policies and aim to provide an environment conducive to active lifestyles.

David Bell, chief inspector, also questions whether schools should be doing more to ensure pupils eat healthily and get enough exercise.

Pollsters FDS International asked 736 parents of five to 16-year-olds how many times a week their child consumed various foods.

When the diets were analysed, 45 per cent of youngsters were categorised as having unhealthy diets, consuming at least five more fatty foods a week than healthy options.

The figures increase as children get older. Among five to 11-year-olds, the proportion eating unhealthily was 39 per cent. For 11 to 16-year-olds, it was 51 per cent.

Among youngsters in the highest social class, the children of professionals and executives, 53 per cent ate healthily, compared with 22 per cent of those whose parents were receiving state support.

High-fat food has been linked with health problems ranging from heart disease to a greater susceptibility to broken bones and bad behaviour in the classroom.

Crisps, identified in the poll as the junk food of choice for the young, are not far behind fruit in popularity, 68 per cent of youngsters munching at least one packet on most days.

The proportion indulging in fizzy drinks most days of the week was 41 per cent; packets of sweets, 39 per cent; chocolate bars, 35 per cent and chips, 17 per cent. However, these figures may actually underestimate the problem, as FDS said some parents appeared to be basing their answers on what they thought their children should be eating, rather than actual consumption.

On average, parents said their children spent more than twice as much time at weekends watching television and playing on computers (nine hours) as they did on physical activity (four hours).

There was some evidence that parents may also be deluding themselves about how fit and active their offspring are.

Six out of 10 of those who said their children did not spend any time at weekends on physical activity nevertheless considered them active.

Seventy-nine per cent of parents wanted a ban on school vending machines.

Among mothers, the figure was 84 per cent.

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