Half of adults will be unable to do the maths needed to understand the new labelling system being launched by the food industry in a £4bn advertising blitz next week, say campaigners.
In an attempt to derail the Government's traffic light warning system for processed food, 21 commercial giants have combined to publicise a rival scheme based on a product's contribution to daily allowances.
The Children's Food Campaign warned yesterday that figures from the Department for Education's skills for life survey suggested that 47 per cent of adults understood percentages so little they would be flummoxed by a scheme designed to improve their health.
Richard Watts, its co-ordinator, suspected the Food and Drink Federation project was a ruse to avoid red warning signs being slapped on junk food. "The food industry will be aware that their new labels will be useless to almost half of adults and most children, who simply lack the complex mathematical skills to interpret them," he said.
On Monday, an unprecedented alliance of food giants will launch a television, press and online advertising campaign called "Know what's going inside you".
Later this month the Food Standards Agency will counter the campaign with 10-second TV advertisements promoting its traffic light system.
Tony Blair warned the food industry last year it faced legislation unless it adopted effective labelling to indicate product healthiness. Most food retailers, including Sainsbury, Asda and Marks and Spencer, have backed the FSA system which uses colours to denote levels of sugar, fat, saturated fat and salt. A green light signifies a low level, rising to amber and then red for a high level.
The rival Guideline Daily Allowance (GDA) scheme is backed by an alliance of food manufacturers including Nestlé, Unilever, Kellogg and Tesco, the biggest food retailer.
The alliance was described yesterday by the £140bn a year food industry as its "biggest ever joint initiative". An industry spokeswoman, Jane Holdsworth, said: "We have made it simple to compare what's inside thousands of everyday foods so you can choose what best suits your diet."
The Food Standards Agency, which carried out research among 2,600 consumers before choosing the traffic light system, said: "We don't have a problem with Guideline Daily Allowances on front of pack but we want to see them accompanied by traffic light colours."
The public agency is spending only a "fraction" of the amount that the food industry has committed to its advertising blitz, prompting fears that the public may be unfairly swayed into backing the GDA scheme. Polling by Which? backed the FSA, finding that 97 per cent of people compared nutrients well using traffic lights. Sue Davies, chief food policy adviser at Which?, said: "Are retailers and manufacturers shying away from using simple, easy-to-interpret colours because they're scared to be up front about the fat, sugar and salt levels in their products?"
The FSA found that 62 per cent of people misunderstood the GDA label scheme, compared with only 21 per cent who misunderstood traffic light labels.