Families need better advice about food and exercise if Britain is to avoid an obesity epidemic, public health experts warned today.

Health professionals need to target advice to parents and children, ensuring that families work together to control their weight, said the Health Development Agency (HDA), which works to reduce health inequalities.

The recommendation came in an HDA report, published today, which analyses methods to encourage people to adopt a healthier diet and lifestyle.

The study, The management of obesity and overweight: an analysis of reviews of diet, physical activity and behavioural approaches, presents a worrying picture of the nation's future health.

Latest figures on childhood obesity from 2001 show 8.5% of British six-year-olds are obese, rising to 15% of 15-year-olds.

About 30,000 people die every year as a result of being obese, according to NHS estimates. Obesity costs the NHS around £2.6bn per year - and this figure is expected to rise to £3.6bn by 2010.

But the chairwoman of the HDA, Dame Yve Buckland, said parents had the potential to make a huge impact on childhood obesity.

"The good news is that the evidence shows parents can successfully treat their child's obesity by actively changing the whole family's approach to diet and physical activity and by avoiding couch potato lifestyles," she said.

Professor Mike Kelly, the HDA's director of research and information, said it was likely the level of childhood obesity had further increased in the past two years.

The professor blamed the country's expanding waistlines on the proliferation of fast food outlets and junk food advertising, as well as unhealthy lifestyles.

"We live in an 'obesogenic' environment - a plethora of fast food outlets, reliance on cars, and offers enticing us to eat larger portion sizes all contribute to the problem," he said.

"The myriad of child-focused food advertising is a real challenge, but parents can fight back. It's them paying at the checkout, not their children."

The professor said simple measures promoted by parents and schools, such as walking instead of driving and simply being more active, could tackle the so-called obesity epidemic.

He also pointed out that obesity was a health inequality issue, with people in the lower social classes most at risk.

Many schools already have programmes to encourage healthy eating and exercise, such as fitness clubs, rules banning chocolate and cake in packed lunches and lessons about diet and nutrition.

The HDA, which is currently drawing up guidelines for tackling obesity with the National Institute of Clinical Excellence, said the most successful methods to reduce weight problems were exercise, better diet, and lifestyle counselling.

Supporting the HDA's evidence, public health minister Melanie Johnson called on food manufacturers and retailers to continue reviewing the nutritional content of foods, and providing better information.

The minister said: "This review once again highlights how crucial prevention is and how simple the message is - that by helping people maintain a healthy diet and an active lifestyle we can stop them gaining weight in the first place.

"We also want to see much more progress from industry to reduce added levels of salt, fat and sugar in processed foods."