What did you feed your child yesterday? Cornflakes for breakfast, perhaps? Marmite sandwiches for lunch? For supper, beans on toast, with a packet of crisps as a snack somewhere inbetween? The menu will vary from household to household, but the chances are that you will have fed your child, and yourself, at least twice as much salt as the recommended maximum level.

Despite growing awareness of the health risks involved with high salt intake, the Food Commission reports this week that many products, especially those aimed at children, are saltier than they were 25 years ago.

So what are the long-term consequences for our health - and why is there so much salt in our diet?

Salt has long been considered a magical substance. In Ancient Rome, it was considered so important to health that a soldier's pay included a special allowance which had to be spent on salt. In the chilly climes of northern Europe, before the development of refrigeration, salt provided one of the few ways of preserving foods to get families through the winter.

And it is well known that a small amount - a tiny amount - is vital for our bodies to function properly, to keep nerve pathways working and maintain our muscles. But in a culture hooked on convenience, processed food, 90% of the population is heavily overdosing on salt which they probably don't even realise is in there.

The Food Commission, which is the UK's leading independent watchdog on food issues, studied the ingredients in white bread, crisps, baked beans and canned tomato soup, comparing the salt content in 1978 with equivalent products selling today. Among the most shocking of their findings was the discovery that salt in crisps has almost doubled since 1978, from an average of 540mg per 100g to 1050mg per 100g. In the rest, there was little improvement, despite industry and government claims that salt has been cut in these processed foods.

Graham McGregor, who is professor of cardiovascular medicine at St George's Hospital, in south London, is an expert on salt. In the past, concern about salt intake has focused mainly on the middle-aged with high blood pressure and heart trouble, but according to MacGregor all of us are eating much too much salt, and the consequences for our health could be dramatic.

"On average we are eating 10-12 grammes of salt a day," he says. " The recommended maximum intake for an adult is 5-6 grammes (one flat teaspoonful). Ninety per cent of the population exceed that, which puts up blood pressure in everybody, which is the major cause of strokes and heart attacks in this country. It's a very major problem.

"If we did reduce total salt intake by the recommended amounts, it would save approximately 30,000 heart attacks and strokes in the UK every year."

In addition to high blood pressure, strokes and heart attacks, which are two of the most common causes of death and illness in the UK, high salt intake is also associated with osteoporosis, fluid retention, asthma and stomach cancer.

The risk is particularly acute in children, who are subjected to intensive marketing of snack and fast-food products that are exorbitantly high in salt. The government's Scientific Advisory Committee on Nutrition (SACN) has recommended that children under seven years should consume an average of not more than two grammes of salt a day. Those between seven and 14 should consume not more than 5g.

"The furring of the arteries starts in early childhood, and children are now eating this appalling diet which is very high in salt," says MacGregor. "People are much less aware they are eating it, but it's all hidden in these processed foods. We are talking about foods that are 20-30% more salty than sea water."

As much as 80% of the salt in our diet comes from processed foods, but why do salt levels need to be so high? "Because it's completely inedible without it. It's totally tasteless," says MacGregor.

"It's to cover up," agrees Anton Edelmann, head chef at the Savoy hotel in London. "It makes up for poor ingredients. It also works as a stabiliser in some foods; it retains the moisture in the food, and keeps it a little bit longer."

Other conspiracy theorists speculate about the links between producers of snack foods and soft drinks - crisp manufacturer Walkers, for example, is a division of PepsiCo which produces Pepsi Cola. Salty foods lead to thirsty children, which in turn leads to increased sales of soft drinks, they suggest.

Steve Chandler of the Snack, Nut and Crisp Manufacturers' Association, which represents companies such as Walkers, KP (makes of Hula Hoops) and Golden Wonder, yesterday dismissed such theories as "total nonsense" and claimed that in the past 10 years, the industry had worked hard to reduce salt levels, which escalated in the late 1970s and 80s with a massive increase in the number and variety of snack produces on the market.

"We've managed to pull it back to the tune of 25% over the past 10 years," he says. "We do listen to what the expert advice is. We do listen to what consumers say. We put a lot of time and effort into trying to improve the nutritional aspects of our product."

The good news is that public awareness is growing. Anton Edelmann used to see customers furiously shaking salt over food he had meticulously flavoured and seasoned in his kitchen. "That's gone nowadays. People are more aware of the fact they should not eat too much salt, but they don't know how to reduce it. In an ideal world I would remove the salt cellar from the table, but I can't do that.

"We all eat more processed food, and that's where the problem comes in. You can't control how much salt you're eating. How can you fight this avalanche of processed foods? People say they have less time so they cook less and buy more ready-meals. I think they should work an hour less and go home and cook proper food."

Tomorrow is National Salt Awareness Day. What a great day to take Anton's advice, knock off early and get home to the cooker.

Watch out for the salt in:

Bread: Just one piece of medium sliced white bread (weighing approx. 36g) contains around 500mg of salt. A six-year old eating two slices will have consumed half the daily recommended salt intake for a child of her age.

Baked beans: An average portion of traditional baked beans (half a tin weighing approx. 200g) contains around 2,500mg of salt, which alone exceeds the daily recommended intake of 2 grams for a six-year old.

Crisps: One 34g packet of Original Hula Hoops containing around 1,000mg of salt would account for half of the maximum daily salt intake of a six-year old.

Tinned soup: One portion (half a tin) of Baxters Tomato Soup (weighing approx. 200g) contains around 2,500mg of salt, which alone exceeds the recommended intake for a six-year old.

Snacks: One Dairylea Lunchable (Harvest Ham variety) contains 2.75g of salt - 37% more than the recommended intake for six-year olds.

Fast food in restaurants: A Burger King children's meal contains 3.3g, which is 65% more than a six-year old should have in one day.

Cornflakes: An average bowl (30g) contains 750mg of salt, almost half what a six-year old is allowed in a day.

Bacon: If your six-year old has a bacon sarnie made up of two rashers of bacon and two slices of bread, she will have consumed 2,400mg of salt, well over her maximum recommended limit. A single rasher of bacon after grilling contains 700mg of salt.

· Statistics provided by the Food Commission