Even supermarket staples can contain terrifying levels of harmful additives – and research published today highlights the cost to the health of our nation's children

Baked beans and beef-burgers; sausages and cereals; pizzas and pita breads are among the most innocuous sounding items we might throw into a supermarket trolley: lunchbox staples and dinner-time essentials that many parents rely upon to keep their offspring happy and their wallets not entirely depleted.

But these foods have a hidden catch, an ingredient whose danger – despite being well-documented by health experts – is still not recognised by the average consumer. Although small amounts of this mineral are essential to life, we take so much that it has become an insidious killer, responsible for more deaths than wars, traffic accidents or illegal drugs. And yet it is kept in kitchens across the country – next to the pepper.

Salt, the secret killer of processed food, is everywhere. We eat two-thirds more of it than we should. Every time we tuck into a sandwich, or a packet of crisps – sometimes even cheese – there is a good chance we are raising our blood pressure.

Worryingly for parents, a new survey out today shows that the processed foods popular with children are loaded with the stuff. It shows that young children eating half a tin of baked beans and two sausages would exceed their recommended salt intake for a whole day in just a single sitting.

According to campaigners, the high level of salt in the British diet kills 35,000 people a year. About 70,000 strokes and heart attacks annually are caused by excess sodium consumption; half end in death. That means the death toll from salt is 10 times more than the 3,172 road deaths in 2006, and the 1,608 deaths from illegal drugs in 2005.

The saltiness of popular grocery items has been uncovered by Consensus Action on Salt and Health (Cash) which previously exposed the hidden quantities in fast food. Researchers checked 73 goods made by the likes of Tesco, Heinz and Dairylea and found dozens of salty products, with up to 4.3 grams per 100g, despite the Food Standards Agency's warning that 1.5g salt per 100g is "high" for adults.

So why is our diet so salty, and what is being done about it?

Many people sprinkle salt into food in the pan or the plate at home. But three-quarters of the salt we consume comes from processed food, where it is used to mask cheap ingredients and enhance weak flavours. The chief victims of this technique are those most likely to tuck into cheap and cheerful meals on a regular basis – children.

With encouragement from the FSA, manufacturers have been reducing the amount of salt in food for the past 10 years. According to the industry, in that time salt in breakfast cereals has been cut by 38 per cent, in cakes by between 16 and 50 per cent and in bread and crisps by 25 per cent. But we are still eating dangerously high amounts. The average adult consumption is about two teaspoons, or 10g a day – two-thirds more than the FSA's recommended maximum of 6g.

Cash found that a child sitting down to half a tin of Morrison's baked beans and two Tesco sausages would eat 4.8g of salt in one meal. A six-year-old scoffing some Bachelors chicken noodles would consume 135 per cent of his 3g daily maximum. Kellogg's Rice Crispies and Dairylea ham and cheese crackers had 1.6g and 1.8g of salt per 100g, enough to earn them a red light under the FSA's traffic light warning system for unhealthy food.

But parents would not know at a glance because most of the big food manufacturers including Dairylea – whose "Lunchables" range is aimed at children – do not put the voluntary labels on their packs. Instead, they use the Guideline Daily Amount percentage system, despite evidence that shoppers find colour-coded traffic lights easier to understand.

According to the British Heart Foundation, this makes it harder for parents to work out which products are high in salt. And many manufacturers list sodium rather than salt. Sodium amounts have to be multiplied by 2.5 to get the figure for salt.

As a result, many parents are confused about which foods are the saltiest, according to a poll by the website Netmum.

Professor Graham MacGregor, Cash's chairman and professor of cardiovascular medicine at St George's Hospital in London, urged manufacturers to step up their efforts to take salt out of food. "Anything that lowers blood pressure in childhood is likely to translate into lower levels of blood pressure in adult life, with reduced risk of developing heart disease and stroke," he said.

"And it's not just heart attacks and strokes that are caused by a high-salt diet. Too much salt is also linked with stomach cancer and osteoporosis and can aggravate the symptoms of asthma.

"If they really cannot reduce the salt content in food eaten by children to reasonable levels, perhaps they should consider ceasing production."

The British food and drink industry is keen to show that it is acting responsibly. An analysis of 100,000 products for the Food and Drink Federation by market research firm TNS Worldpanel showed that, in the past 12 months, 2,000 tons of salt had been removed from crisps, breakfast cereals, bread, home cooking products, and canned goods. Peter East, a director of TNS Worldpanel, said the average consumer purchased 0.3 per cent less salt in 2007.

But the Salt Association, which represents the salt industry, fiercely disputed any suggestion that high salt consumption causes heart problems. Describing Cash's claims as "shoddy", the association said: "Any correlations between food intake and health are simply statistical associations and not evidence of causation."