Parents are being urged to plan their children's diet with care as the Government published its "most accurate figures" yet on how the English are turning into a nation of fatties.

By 2010, more than 12 million adults and more than 1 million children will be classified as obese unless preventive measures are taken, according to a Department of Health report, Forecast for Obesity to 2010.

According to official figures, obesity is already a problem for 22 per cent of the male population over 16 (4.3 million) and 23 per cent of women (4.8 million).

An adult is considered "obese" if their body mass index - their weight in kilograms divided by the square of their height, in metres - is 30 or above.

Millions more are classed as "overweight", meaning they have a BMI of 25 to 30. By 2010, the figures are set to soar to 33 per cent of men (6.6 million) and 28 per cent of women (6 million).

At present, obesity is more common among boys under 16 than among girls, but the projections suggest that, by 2010, the proportion of obese girls will have risen from 16 per cent to 22 per cent, and of boys from 17 per cent to 19 per cent.

"With children heading back to school in September, these statistics should give parents food for thought on how to make their kids' lifestyles healthier," said the Health Secretary, Patricia Hewitt. "We are intervening and helping to make a difference, but we want today's figures to act as a stark reminder of the problem we and our children will face if we don't act now and start making healthier lifestyle choices."

The Government has been promised co-operation from the food industry, which warned that there was no "silver bullet" that could instantly solve the problem.

"Food is only one factor in an extremely complex situation," said Julian Hunt, director of communications of the Food and Drink Federation. "Manufacturers are introducing better labelling to help consumers understand what's inside the food they are buying.

"At the same time we have made tremendous cuts in salt, sugar and fat in foods. Additionally, the food and advertising industries have put forward a radical set of proposals which will see no more advertising of any branded foods during children's programming on terrestrial TV.

"But a key part of any programme to effect lifestyle change is getting people to understand that they need to balance the calories they take in with the calories they expend through exercise."

Bar Hewlett, a founder of the weight-loss programme LighterLife, said: "The Government is right, but the problem needs to be addressed at source - many people overeat for psychological reasons, often rooted in their childhood."

Tam Fry, board member of the National Obesity Forum, said: "The figures are tragic but no one should be surprised. The Government has been announcing for years what needs to be done to fight the nation's fat - but then has done very little to achieve it."

Earlier in the week, the public health minister, Caroline Flint, was designated "minister for fitness" with a brief to tackle obesity.

Sandra Gidley, for the Liberal Democrats, said yesterday: "This week's rebranding of Caroline Flint as 'fitness minister' was a gimmick intended to shift attention away from the Government's failure to tackle the timebomb of obesity in this country.

"Obesity is one of the issues which she should already be dealing with as the minister responsible for public health.

"The Government has created measures for GPs to identify obesity but have not backed them up with concrete resources to actually tackle the problems."