The Scottish Government has been urged to take action and outlaw supermarket junk food promotions.

Several of the nation's top doctors and public health experts have come together to sign an open letter in a bid to tackle the country's obesity problem.

The group, which includes a paediatrician and a liver cancer specialist, is pushing for legislation this year.

The letter, which points out that 65% of Scots and almost a third of the nation's children are overweight, calls for urgent action in September's Programme for Government.

With Scots among the heaviest in Europe, excess weight is the biggest preventable cause of cancer after smoking and causes around 2,200 cases of the disease every year.

Obesity is linked to 13 types of cancer including bowel, breast womb and kidney.

The letter has been signed by:

• Professor Linda Bauld, chair in behavioural research for cancer prevention at Cancer Research UK.

• Professor Steve Turner, Scottish officer of the Royal College of Paediatrics and Child Health, University of Aberdeen

• Dr Tom Bird, honorary consultant hepatologist, Royal Infirmary of Edinburgh; intermediate Wellcome Trust fellow, University of Edinburgh; senior clinical lecturer, University of Glasgow

• Elma Murray OBE, chair of the Scottish Obesity Alliance

• Lorraine Tulloch, programme Lead, Obesity Action Scotland

The letter increases pressure on the Scottish Government to take bold action on obesity as soon as possible.

It says: "Scotland is a nation in the midst of an obesity epidemic.

"The Scottish Government must take action and commit to legislation in this autumn's Programme for Government to regulate multi-buy type price promotions of food and drink high in fat, sugar and salt.

"Every day in Scotland an overwhelming 110 tonnes of sugar are purchased on promoted offers such as 3-for-2 chocolate bars or buy-one-get-one-free mega bags of crisps which are of no nutritional value.

"Research shows that shoppers who purchase more on promotion are more likely to be overweight or obese. We also know that two-thirds of Scots support restrictions on multi-buy promotions. The case is compelling. Now's the time to act and turn the tide on obesity. The health of our nation depends upon it."

Gordon Matheson, Cancer Research UK's public affairs manager in Scotland, said: "The voice of both expert and public opinion is clear.

"Price promotions on junk food encourage people to fill their shopping trolleys with unhealthy food which is eaten all too quickly.

"New laws to restrict junk food price promotions will take away the temptation that's contributing to this obesity crisis and go a long way to helping people to keep a much healthier weight.

"The consequences of obesity on the lives of children and adults in Scotland is shocking so it's vital the Scottish Government commits to legislation this year."

A Scottish Government spokesperson said: "Tackling obesity is a public health priority and our Diet and Healthy Weight Delivery Plan already includes a wide range of bold measures designed to help families make healthier choices.

"We are currently considering responses to our consultation on restricting the promotion and marketing of discretionary foods high in fat, sugar or salt with little or no nutritional benefit. This will help us consider which potential actions we take in this area in future."