The Liberal Democrats want food sold in shops to be marked with green, amber or red "traffic lights" to inform consumers how healthy it is.

Health spokesman Paul Burstow said the scheme would give shoppers the opportunity to choose food that is lower in sugar, fat and salt, and would shame producers into making their goods healthier.

And he indicated that the Lib Dems would be ready to see government take action to force producers to cut unhealthy ingredients if traffic-light labelling did not work.

Mr Burstow was speaking as the Co-Op began a trial of new labels detailing the calorie, salt and fat content of major branded goods like biscuits and cakes.

He told the BBC Radio 4 Today programme: "What we need to see is the Food Standards Agency taking forward the idea of traffic-light labelling, which the Liberal Democrats want introduced, and making sure that the scheme is clear and consistently applied across the food products and all food companies.

"We think there is a need to look at how we can use the traffic-light system to address such issues as the level of salt in food, sugar in food and fat in food."

The scheme could be based on the concept of "energy density", which reflects the ratio between the weight of a product and the number of calories it delivers, targeting products like crisps which are light in weight but very fattening.

"The first step is to realise that introducing a traffic-light labelling system will put an immense amount of pressure on the industry," he said.

"There aren't going to be many manufacturers of foods who are going to want to have a red light on the foods that are being served up."

Asked if the Lib Dems would place a statutory duty on producers to make food healthier if they did not do so voluntarily, Mr Burstow said: "I think we do have to be clear to the industry that, if they are unable to respond to pressures in the market - and there is clearly consumer pressure now to see reductions in these areas - then Government may well have to step in."

Tuesday September 21, 2004