A public health expert has called for chocolate bars and other snacks to be made in smaller sizes to help reduce heart disease.

Dr Malcolm Law told a Royal Society of Medicine conference that the food industry could introduce changes that could have an impact on public health.

He said pizzas, chocolate bars and ice creams had all got bigger in recent years.

Often a small or regular snack was virtually the same price as a larger version, plus there were now more "buy one, get one free" offers.

Dr Law, an epidemiologist from the Wolfson Institute of Preventative Medicine, which is part of Barts and the London Medical School, said cutting portion sizes would have a "worthwhile impact" on coronary heart disease.

Research where people were given different sized portions suggested most felt they had to clean their plate even if given a large amount.

Dr Law said: "No one food manufacturer would make changes on its own but if the Food Standards Agency or Govern-ment negotiated with the industry and suggested reducing portion sizes it would be in the interests of public health."

Chocolate maker and retailer Thorntons sounded a cautious note about its prospects after sales growth stalled over the Christmas period.

Like-for-like sales dipped 0.9 per cent in the seven weeks to December 28 after the company had enjoyed growth rates of 5.8 per cent in the previous six months and posted growth of eight per cent over the same Christmas period last year.

Chief executive Peter Burdon described the festive season as "tough" and said interim profits would now be at the lower end of market expectations.

Total company sales were £104.7 million in 28 weeks to January 11.