Fresh calls have been made for a crackdown on the sale of junk food as research suggests obesity is set to overtake smoking as the biggest preventable cause of cancer among UK women.

Campaigners say the projections also strengthen the case for a wider calorie labelling and calorie limits on takeaway food.

The calculations, drawn up by epidemiologists at Cancer Research UK, predict that the number of female cancer cases in the UK linked to obesity will exceed the number caused by smoking for the first time in 2045.

It reflects a long-standing decline in smoking rates, while the percentage of adults who are overweight or obese has been climbing.

Overall in Scotland, obesity rates in adults are around a fifth (19%) higher now than in the early 2000s. Meanwhile, smoking rates among adults have dropped by a quarter (26%) over the same period of time.

On current projections, 10% of cancers in women - around around 25,000 cases a year - are expected to be caused by smoking in 2035, compared to 9%, or around 23,000 cases, from being overweight or obese.

However, by the early 2040s they are projected to even out and by 2045 obesity will nudge ahead, causing more than 26,000 female cancers.

Excess weight is linked to an increased risk of 13 different types of cancer, including breast, bowel and kidney.

Among men, smoking will continue to be the leading cause of cancer but the gap is narrowing. Around 35,000 cases of cancer will be due to smoking in 2026 compared to 15,000 linked to overweight and obesity. By 2035, smoking will be responsible for around 34,000 male cancer cases, but excess weight will cause around 22,000.

Professor Linda Bauld, an expert in cancer prevention and public health based at Stirling University, said new laws are needed to make food shopping a healthier experience for families.

She said: “While the results of this study focus on the UK picture, unfortunately the forecast is expected to be similar for women in Scotland.

“It’s positive the Scottish Government has signalled its intention take action on obesity and will consult on plans to restrict an array of supermarket price promotions.

“Junk food multibuy offers encourage us to bulk buy and eat large quantities of unhealthy food, the consequences of which have become all too obvious in the nation’s growing waistlines.

"The public wants action and the introduction of laws to curb bargain buys for food and drink high in fat and sugar would be an effective way of helping people make healthier choices.

"The Scottish Government can and must take action - it has a duty of care to protect future generations from the health problems we're seeing because people are carrying too much weight."

The Scottish Government has outlined plans to restrict the promotion and marketing of junk foods including confectionary, biscuits, crisps, cakes, and sugary soft drinks.

It would ban retailers from offering multi-buy deals, meal deals, and unlimited refill deals including these items, and target food venues such as restaurants, takeaways and cinemas by requiring them to display calorie information on menus and potentially restricting the portion sizes they can sell.

Opponents have warned the measures would "punish" small businesses and make food shopping more expensive for the poorest consumers.

Public Health Minister Joe FitzPatrick said: "Cancer Research UK's support for our plans is very welcome as we know that as a nation, we consume too much food and drink with little to no beneficial nutritional value to our diet and contain considerate calories or salt. As this study shows, that has serious implications for the nation's health.

"This autumn we will consult on world-leading measures to restrict promotions of junk food where they are sold, such as multi-buys, which encourage over-consumption. Consumer spending on price promotions in the UK is the highest in Europe, so it is right we take action."