Six major food suppliers, including Tesco, have been condemned by a government watchdog for rejecting a recommended nutritional labelling scheme that is designed to encourage healthy eating.
Dame Deirdre Hutton, the head of the Food Standards Agency, accused the companies of "choosing to ignore the weight of evidence" by dismissing its advice.
The six - Tesco and five of the world's largest food manufacturers - have banded together to develop their own nutritional labels.
They rejected the agency's recommended use of traffic light colours to show high, medium and low levels of key nutrients. A red logo on the packet would signify high content in salt, sugar or fat; amber would suggest moderate consumption while green would equate to the healthiest.
Instead, they have opted for labels which show the recommended guideline daily allowances (GDAs) of nutrients such as fat, saturated fat, sugar and salt.
In a speech to the National Federation of Women's Institutes in Cardiff, Dame Deirdre praised Sainsbury's and Waitrose for bringing in the recommended traffic light-coded labels. Asda is among other companies set to follow suit.
She said the system was the result of independent research carried out among 2,600 people and questioned why the six companies had chosen not to follow its recommendations.
"You may have heard that some manufacturers have gone off and developed their own front-of-pack schemes not using traffic light colours - so not in line with what we'd like to see.
"Tesco is one; and five of the world's largest food manufacturers have banded together to do something similar: Danone, Kellogg's, Kraft, Nestlé and PepsiCo. It is good news to see progress on front-of-pack labelling, given the objections there were to it only a year or two ago. But you have to wonder why these companies are choosing to ignore the weight of evidence and not use traffic light colours in their schemes."
Dame Deirdre called on shoppers to write to retailers and manufacturers to ask about labelling policies.
Jane Holdsworth, director of the GDA campaign, defended the departure from the FSA-backed labelling system. "Our industry research conducted among 1,700 shoppers earlier this year showed that nearly nine out of 10 consumers believed the GDA front-of-pack, at-a-glance scheme, now appearing in stores, was both clear and simple," she said.
A Tesco spokesman said it was the first to start putting nutritional labels on products more than a year ago, and suggested they were far simpler for the consumer to understand than the traffic light scheme.
"Tesco nutritional signposts are easy to understand and sales data shows they are already leading customers to make healthier choices. Traffic lights may never produce these results. They can also have perverse effects on some products, for example, both cola and apple juice would be colour-coded amber for sugar - confusing customers and ensuring they ignored the information," he said.
Kellogg's said the first of its GDA labels had already started appearing in stores. Earlier this week, Tony Palmer, managing director of Kellogg's UK, defended the use of GDA labelling. "GDA labelling is the clear consumer preference for front-of-pack nutritional information as they give consumers easily accessible information to guide their choices," he said.
"Labelling has been a hot topic and the food and drink industry has committed to GDAs on pack with about 80 per cent of cereal manufacturers, and the majority of all other packaged foods having the new labelling on by the end of this year."
A spokesman for Unilever said it was set to introduce GDA labels on about 1,000 products including Flora spread, Birds Eye peas, PG Tips, Walls Solero and Hellmann's mayonnaise.