Ready meals for children and "healthy options'' foods contain "unacceptably high" levels of salt, a government survey alleged yesterday.

The Food Standards Agency accused leading supermarkets of misleading customers and risking their health by adding too much salt to their products. The agency's survey found that nearly half of prepared meals for one contained more than 40 per cent of the maximum daily salt intake.

Even meals promoted as healthy options for children - such as the shepherd's pie from Sainsbury's Blue Parrot Café range - had more than a third of the daily salt intake in one serving. The supermarket claims that Blue Parrot meals have "controlled salt levels", but the shepherd's pie had the fourth-highest level among the children's meals tested by the agency.

Adult meals aimed at dieting consumers are even worse. A lasagne from Asda's "Good For You" range was found to have 3.6g of salt - almost two thirds of the recommended intake.

The worst offender was Sainsbury's standard shepherd's pie, which had 6g of salt, the entire recommended daily intake for adults. Overall, Asda meals contained the most salt, while Tesco products had the least. Sir John Krebs, chairman of the agency, said: "It isn't acceptable for ready meals loaded with salt to be called 'healthy' options. They are far from it and mislead consumers. The food industry has a responsibility to be honest with consumers and we will be checking again next year to see what progress they have made. It is possible to reduce the amounts of salt in ready meals. Convenience shouldn't mean an increased health risk."

The agency issued the first guidelines on salt intake last month amid concerns that most people ate far too much salt. Children aged four to six should not eat more than 4g of salt a day, while those aged seven to 10 should have a maximum of 5g.

Research has shown that on average adults eat 9g of salt a day. High salt intake has been linked to an increased risk of heart attacks, strokes, osteoporosis and stomach cancer. Experts say that if salt intake was reduced to recommended amounts, there would be 30,000 fewer heart attacks and strokes in the UK every year.

People have been urged to use less salt when cooking but three quarters of the typical adult's consumption is "hidden" in processed food. The Food and Drink Federation has made a commitment to reduce salt in products such as food and sauces. Now the agency wants manufacturers to make a similar commitment on ready meals. Salt is often added to meals as a stabiliser to retain moisture and extend shelf life. Critics of the food industry say salt is also pumped into processed products to make up for inferior ingredients.

Professor Tom Sanders, head of nutrition at King's College London, said: "Some of these meals are like eating sea water. The people most at risk are the over-fifties. They are a problem as they are more likely to buy healthy-eating ready meals, thinking it is going to do them some good."

An Asda spokeswoman said: "Obviously the results are disappointing ... in the light of the guidelines ... [we] will be doing more to reduce salt levels."