Professor Martin Wiseman, medical and scientific adviser at the World Cancer Research Fund (WCRF), has warned the UK is �sleepwalking� towards more cancer cases than ever before.

Cancer rates could double within the next 40 years unless obesity is tackled, health experts warned yesterday.

Professor Martin Wiseman, medical and scientific adviser at the World Cancer Research Fund (WCRF), said the UK was "sleepwalking" towards more cancer cases than ever before, and action to curb rising obesity rates was essential.

Speaking before a conference that will highlight the extent of the problem, Professor Wiseman said the latest figures suggested one-third of women and half of men would be obese in the next 40 years.

Excess body fat is linked to cancer of the bowel, breast, womb, oesophagus, kidney and pancreas.

He added: "The evidence now shows that, after not smoking, maintaining a healthy weight is the most important thing you can do for cancer prevention. This means that if rates of obesity continue to rise, then this will have serious consequences for cancer rates in the UK.

"Unless something happens soon to stop the increase in obesity, then we are sleepwalking towards a situation where the UK will be facing more cancer cases than ever."

The statistics are of particular concern in Scotland, which is second only to the US in obesity rates. In Scotland, almost one-third of all 13 to 15-year-olds are overweight, while nearly 10% are considered severely obese.

As reported in The Herald on Saturday, severely obese teenagers could soon be eligible for weight loss surgery, such as gastric bands, on the NHS under new draft guidelines for doctors.

In the US, the number of such operations performed on teenagers has almost tripled in the last three years. Last year, more than 1000 morbidly obese young people in America underwent what is known as "bariatric" surgery.

At least three teenagers in Scotland are said to have had similar operations. The three, all girls, a 16-year-old weighing 33 stone, a 17-year-old at 24 stone, and an 18-year-old at 21 stone, are believed to have had gastric bands fitted.

Scottish clinicians say they are now dealing with cases of type 2 diabetes in adolescence, something unheard of even seven years ago.

Dr David Haslam, clinical director of the National Obesity Forum, said he was not surprised at the latest figures, though he believed the public would be.

He said: "The country is indeed sleepwalking towards an obesity epidemic, and we are desperately trying to wake people up. It is astonishing that despite all the medical advances made, life expectancy is falling due to obesity.

"We should also remember that obesity can also cause Alzheimer's disease, adult blindness, and infertility. We need to push the healthy eating message through schools and the food industry, and make exercise more accessible to all."

Liberal Democrat health spokesman Ross Finnie described the WCRF figures as "shocking". He added: "We already know that obesity is contributing to a dramatic increase in the levels of type 1 and type 2 diabetes. But these are shocking statistics.

"It's more crucial than ever to target young people and make sure that they have better diets and take more exercise."

A spokeswoman for the Scottish Government said ministers were taking steps to address the country's worsening obesity problem.

"Tackling obesity, particularly in early life, is a high priority. We know obesity poses a serious threat to health and increases the risk of developing chronic illnesses such as cancer, heart disease and diabetes, she said.

"Backed by £56m, our obesity action plan supports a wide range of initiatives dedicated to promoting healthy eating and physical activity."