Britain's giant supermarket chains are in open conflict with the Government over unhealthy levels of salt in the food they sell.

Britain's giant supermarket chains are in open conflict with the Government over unhealthy levels of salt in the food they sell.

Sainsbury's and other shops have angered ministers by flatly refusing a direct request to improve their plans to cut back on salt, which is implicated in health problems.

The Government launches a national campaign this morning to persuade consumers to lower the salt intake in their diet, as its contribution to high blood pressure is thought to lead to 70,000 heart attacks and strokes each year. "Too much salt is bad for your heart," the campaign advertisements will warn.

But a demand from the Public Health minister, Melanie Johnson, for food retailers to update their salt reduction plans by the end of the week has been met with a resounding raspberry.

Sainsbury's, Waitrose, Asda and Iceland have all ignored the request and are continuing to work on the less rigorous salt reduction strategies they formed at the start of this year. Tesco, the UK's largest food retailer, said it had not received Ms Johnson's 16 June letter containing the call and, as a result, would not respond to it.

"Melanie Johnson has asked us to submit a revised action plan, but we are not going to do that," said Erica Zimmer, a spokeswoman for Sainsbury's.

"We are not going to meet that deadline because we believe our action plan is fine. We agreed it with the Food Standards Agency. We are making good progress to achieving the target we set ourselves."

Nutritionists have long warned high levels of salt are linked to high blood pressure, which substantially increases the risk of heart disease and strokes. The average adult effortlessly exceeds the recommended daily intake of 6g of salt, by consuming 9.5g. The average school lunch box contains up to half the daily recommended intake, and certain pizzas contain almost three-quarters of an adult's daily allowance. Studies have shown that reducing levels of salt in the diet can lower blood pressure within four weeks.

Ministerial vexation with the hugely profitable retailing giants ­ Sainsbury's made over £600m last year ­ is growing. "Their refusal to meet the deadline [for a new plan] is silly, and we are extremely disappointed," said a source close to John Reid, the Secretary of State for Health. "These issues are of crucial concern to their customers."

The supermarkets' failure to move has been even more fiercely criticised by Professor Graham MacGregor, the head of the blood pressure unit at St George's hospital in London and chairman of the anti-salt pressure group Cash (Consensus Action on Salt and Health).

"The response from the food industry so far, quite frankly, has been pathetic," he said. "For every 10 per cent reduction we would save 7,000 deaths a year. You could make a 15 per cent reduction in all of these foods tomorrow and there would be no taste or safety problems, no technological problems."

Behind the row lies growing tension as the Government wants to make faster progress in meeting public health targets to be set out in a forthcoming White Paper. "[Retailers] are locked into a taste battle with each other and want more time to get people weaned off salt," a ministerial source said.

Health ministers believe consumers will be defeated in their efforts unless the stores and food suppliers themselves do more to cut down on the salt in a wide range of products, from soups and pizzas to cornflakes.

Ms Johnson upset retailers in June when she told them their salt reduction plans were too vague, and ordered them to submit revised plans by 18 September. She wrote: "So much more concerted action is needed if we are to meet our aim to reduce the population average intake [of salt] to six grams a day ... From the plans already submitted, about 50 per cent of the products such as pizzas, sandwiches and ready meals will continue to contain unacceptably high levels of salt. I would like to see across-the-board reductions."

The British Retail Consortium's director general, Dr Kevin Hawkins, wrote in a reply to Ms Johnson's letter that "a relatively long period of time will be needed to bring about the cultural shift in the attitude of many consumers to salt intake".

A Cash group study revealed last week that own-label supermarket products were among the saltiest foods.