Children are to be given a little of what does them harm in the biggest trial of immunotherapy for peanut allergy conducted.

The £1 million British study follows earlier research indicating that peanut allergy can be overcome - with peanuts.

Gradually building up tolerance with small amounts of peanut protein appears to dampen down the potentially dangerous allergic reaction.

Now the idea is to be tested for the first time on a large scale with 104 British children aged seven to 17 suffering from peanut allergy.

Their "medicine" will be increasing doses of peanut flour added to yoghurt.

Tiny quantities of peanut, starting at about one milligram, will be built up slowly until the children are eating the equivalent of five nuts a day.

Some of the children are severely allergic and would normally be at risk of life-threatening symptoms from such exposure.

Dr Andrew Clark, from Cambridge University, who is leading the study, said: "This is going to be the largest trial of its kind in the world and it should give us a definitive idea of whether the approach works and whether it's safe.

"It's based on our successful pilot study where we showed 21 out of 23 kids were effectively desensitised to peanuts."

Allergy to foods such as peanuts can induce a potentially fatal inflammatory reaction called anaphylaxis.

Nut allergy is the commonest cause of anaphylaxis among younger age groups, placing around one in 50 children at risk.

The number of children vulnerable to the reaction has increased dramatically in the developed world over the last 10 years.

In the US, food allergy prevalence among children soared by almost 20% during the decade.

Dr Clark's pilot trial recruited 23 children shown to suffer an allergic reaction to the equivalent of less than one peanut.

They were started off on one milligram of peanut each day, increasing the amount every two weeks until they could tolerate five nuts, or 800 milligrams.

This amount was then taken daily as a maintenance treatment for at least six weeks.

Most of the children responded well, despite developing short-term mouth itching or stomach pains when doses were increased.

All but two children were eventually able to eat at least five peanuts a day with no ill effects, said Dr Andrew.

Six months after the start of the study, 83% of the group were able to tolerate 12 peanuts at one go. A year on, 88% could safely eat 32 peanuts. As a result they no longer had to screen food labels and be wary of what they were eating.

Speaking at the annual meeting of the American Association for the Advancement of Science, Dr Walker said: "The families involved in this study say that it's changed their lives. It's dramatic. Whereas before they were checking every food label every time they ate food.

"They would worry it would cause a reaction or even kill them but now they can go out and eat curries and Chinese food and they can eat everyday snacks and treats.

"For their birthday they can have chocolate cake and chocolates without any fear of reactions. So that's our real motivation - to try to develop that as a clinical treatment that we could spread to the rest of the country.

"Our long-term aim is to keep them going with weekly dosing as that might represent what you would normally eat in peanut consumption, and they feel comfortable with it."

The new trial, funded by the Department of Health's Institute of Health Research, will run for three years.

If the study is successful, consideration will be given to making the treatment widely available, said Dr Walker.

But he warned that no-one should be attempted to "have a go" at peanut therapy without supervision.

"This is currently a research treatment which requires intensive clinical input and must not be tried at home outside the research setting," he said.

"I think in two or three years time we will be in a position where we have a treatment that works but we are still working on a long term cure.

"It's likely to be a treatment that lasts at last two or three years and we hope that once that's over we can withdraw the treatment and maintain long term tolerance. But we need a long term study to find out."