This has been attributed to a diet of junk food and a couch potato lifestyle, which say the experts promises the possibility of severe health problems in later life.

According to official statistics, a third of Scots children were classed as overweight before they hit their teens, one in five was obese and more than one in ten was rated as severely obese.

Neville Rigby of the International Obesity Taskforce, an independent body that brings together obesity experts, says the figures class twenty percent of Scottish children as obese and in the same league as the U.S.

Rigby, the taskforce's director for public affairs, says high rates of obesity are seen in other countries, especially southern Europe, but what is being seen in Scotland is a worrying trend.

Scottish Health Statistics figures show that among Scottish children born in 2001, 20.7 percent were overweight before they were 4 years old.

Experts say that though no one factor causes childhood obesity a poor diet and a lack of exercise are considered key problems.

Dr Beckie Lang, a public health nutritionist at Britain's Association for the Study of Obesity, says there is a correlation between low income and poor food choices, and obesity often tracks deprivation.

She says there is a problem of filling up on cheap, poor quality food.

Levels of obesity in Scottish children rose over the last five years and have significantly surpassed levels anticipated 15 years ago when it was expected that 15 percent would be overweight, 5 percent obese and just 2 percent severely obese.

Scotland has often been called "the sick man of Europe" for a health record which does not compare favorably with other European countries.

According to Dr Toni Steer, a nutritionist at the Medical Research Council (MRC), says heart disease and cancer rates in Scotland support that view.

The report warns that being overweight or obese during childhood may lead to physical and mental health problems in later life, such as heart disease, diabetes, osteoarthritis, back pain, low self-esteem and depression.

Rigby says more work needs to be done and the main issue is diet and children need to be eating better quality food and encouraged to move around more on bikes and on foot.

Rigby says that children face a "barrage" of advertising and marketing from the fast-food industry which is not helpful.