The restaurateur Sir Terence Conran condemns Britain's obsession with hygiene today and says too much cleanliness is making the nation ill.

In a letter to The Independent, he says there are so many rules and regulations in place to prevent dirt from getting into our bodies that the British have lost the ability to fight off disease and are increasingly suffering from allergies and stomach upsets.

According to the British Allergy Foundation, the number of sufferers is going up by 5 per cent every year, and as many as half of them are children.

No one knows exactly why the number of allergy sufferers is increasing so quickly but one theory is that the cleaner environment that children are now brought up in does not challenge their growing immune systems.

In his letter, Sir Terence says: "We, and our Government and the EU, have all conspired to do everything we can to kill off those antibodies and bacteria that used to fight our battles for us. All sorts of rules and regulations and official bodies and bureaucracy are now in place to prevent that legendary 'peck of dirt' getting into our system.

"The result of all this hygiene is that we become more and more sensitive to illness and bacteria, and viruses develop and find ways to survive every new scientific assault...

"I always have the vision of the typical British family, cosseted on a diet of clinically prepared oven-ready microwaveable food with an absurdly short sell-by date, prepared in a hygienic and bacteria-free environment, falling dead after eating a couscous in a kasbah in Tangier whilst all the Arabs around them are healthy and happy with their pecks of dirt fighting their gastro-battles."

Government health bodies advise people to pay close attention to supermarket use-by dates and to wash their hands when preparing food but scientists have found that the children of farmers suffer less from allergies, hay fever, wheezing and asthma. This is thought to be because they are exposed to bacteria and microbes in infancy which toughens their immune systems.

Rose Gray, who travels round tiny villages in Italy seeking traditional recipes for the River Café in west London, said that hygiene was important but that she did have some concerns that it had gone too far. She said: "The one thing that does worry me is that if the EU regulations means that dairy foods like milk and cheese all have to be pasteurised, children who are used to that could have a problem if they then eat unpasteurised food.

"There is no doubt that the rules of the kitchen have become stricter - at one time we weren't allowed to use wooden spoons and then it was decided they were all right after all - but those rules are designed to help not hinder."

A spokesman for the Public Health Laboratory Service said: "It's not about getting rid of all the bacteria but learning when to intervene to avoid the dangerous ones. One of our main concerns is that people do think they need to live in a sterile environment but that is not desirable, or possible. We need some bacteria around. There are benefits to good hygiene but we certainly don't think that all bacteria need to be obliterated."

But Ann Goodwin, of the Chartered Institute of Environmental Health, said consumers were right to worry about hygiene and should pay attention to supermarket use-by dates. Ms Goodwin said: "A lot of people do worry that we are taking cleanliness too far but there are a number of emerging pathogens [dangerous bacteria such as E.coli 0157] which only need a very small amount to cause an infection. Two E.coli bacteria can kill a child and 10 can make an adult very ill, so nowadays it is absolutely crucial to be careful and to wash your hands.

"We are much more circumspect these days but it is right to be so. Consumers have demanded fewer preservatives in food so the shelf-life of many products has decreased and you must pay attention to the dates on the packaging which has been carefully worked out."