The Government is threatening action against some of the country's major food companies - includingSainsbury's, Waitrose, McDonalds, Heinz and Nestlé - for failing to cut salt in processed food.

The Health Minister, Melanie Johnson, has warned more than 20 companies that if they fail to come up with improved proposals by September, the Government will likely introduce compulsory warnings on high-salt products.

"This is their final chance really," a Department of Health spokesman said last night.

The companieswere asked by the Government at a summit in February to come up with proposals for drastically reducing salt in their foods, in a bid to act against heart disease.

The companies have since come up with plans, and some have made salt reductions, but the Government does not believe the proposals are adequate. "We have written to some of the major food manufacturers, just saying their plans to reduce salt don't go far enough," the DoH spokesman said. "They have had quite a while to submit proposals. The recommended daily intake of salt is six grams, but some ready meals can contain 80 per cent of that."

Waitrose, Asda, Sainsbury's and Marks & Spencer have been targeted in terms of their "own" brands. Also on the Government's shame list is the school meals company Scholarest, as well as United Biscuits, Northern Foods, Iceland, Kraft, Unilever, Safeway, Cadbury Schweppes, and even the MoD Defence Catering Group.

The Government has said that research shows that 70,000 strokes and heart attacks, more than half of which lead to death, would be prevented if the average salt intake was reduced to six grams a day.

Ms Johnson wrote telling the companies that salt levels should be cut by up to 45 per cent in products such as sausages, beefburgers, bread and breakfast cereals.

"The plans are too often short on detail and specific actions," Ms Johnson wrote.

"What is needed are real commitments across the board for key product categories such as pizza, breakfast cereals, sandwiches and ready-made meals to ensure that we reach the necessary reduction in salt intakes from processed foods.

"From the plans submitted around 50 per cent of the products, such as pizzas and ready meals, will continue to contain unacceptably high levels of salt."

The Department of Health confirmed last night that the Government is looking for an average 40 per cent cut in salt in beefburgers, 20 to 40 per cent in bread and cereals, 43 per cent in sausages, 38 per cent in ready meals and 33 per cent in baked beans.

But some of the companies which were named and shamed last night were upset that it had not been recognised that they had made salt reductions, according to The Times.

Marks & Spencer said it had cut salt in bread by 20 per cent, in ready meals by 30 per cent, grocery products by 20 per cent and pizzas by 9 per cent. McDonalds said it had cut salt in children's Happy Meals by 20 per cent, in chicken McNuggets by 30 per cent, french fries by 24 per cent and ketchup by 23 per cent.

MPs have previously called for new labelling or the banning of some food advertisements aimed at children if salt is not reduced, but Ms Johnson only addressed the issue of compulsory warnings on high-salt products in her letter.

"We have said we want to see revised plans by September, then we'll see what they're like and consider what action we can take on this," the DoH spokesman said.