Ian Ellison, one-time keeper of 50,000 bees, qualifies as one of the luckiest men around. In May last year, he was cutting the grass in his back garden when he felt a sharp pain in his cheek. He ran indoors, realising that he had been stung by one of the bees he kept in a colony in the garden.

It was his second season of beekeeping, and he had never been stung before the previous day, when he had been stung twice. However, he did not know that he was among the estimated one in 200 people who are allergic to wasp or bee venom. He found out very soon.

Mr Ellison knew it was important not to rub the sting and to try to remove it, which his wife did with a pair of tweezers.

He had a cup of tea and went outside to resume cutting the grass. Within 10 minutes he had collapsed and passed out. His wife rang for an ambulance. When the paramedics arrived and were told what had happened, they realised Mr Ellison, a 51-year-old chartered accountant, was suffering from anaphylactic shock. It is likely that the first two stings had sensitised his body to the allergen, with the third triggering the immune overreaction. The paramedics immediately gave him an injection of adrenalin, which probably saved his life.

People who go into anaphylactic shock, a severe and life-threatening allergic reaction, are hypersensitive to foreign proteins. They experience a sharp fall in blood pressure and an escape of fluid into the tissues. The treatment is immediate injection of adrenalin or steroids.

'Most people develop an immunity to stings from insects and although I had been bitten before, I had not been stung by a bee. This was the first time anything like this had happened,' says Mr Ellison.

Mr Ellison had always worn protective clothing when working on the hives. But at the time of the attack, he had only been wearing everyday clothes.

Like many others, Mr Ellison had no inkling of his allergy and would never have put himself at such risk. His wife has since insisted that he give up beekeeping.

Many who suffer from the allergy are afraid to go out of doors from July to September, the peak time for wasps and bees. But they can be helped.

Exactly how many die is hard to estimate. The Office of Population, Censuses and Surveys records up to 10 deaths a year from insect or snake bites. One in 10 people questioned at random report having been stung in the past year, according to Dr Lawrence Youlten, a consultant at the chest clinic at Lewisham Hospital, south London.

Dr Youlten helps to run one of only three venom immunotherapy clinics in the country at Guy's Hospital, London, together with Professor Tak Lee. The clinic treats patients who have an allergy to bee or wasp venom, and currently has a 17-week waiting list for an initial appointment.

Patients such as Mr Ellison are referred to the clinic by their GP for a course of desensitisation. The clinic treats around 15 patients a week. The treatment involves injecting the patient with a small amount of venom every week for three months and then once a month for two to three years in order to build up immunity.

'When a person with an allergy is stung, they suffer anaphylactic shock, which is caused by the number of antibodies introduced into the blood,' says Dr Youlten.

'This is a huge cardiovascular event. Younger people may well faint and lose consciousness because of the sudden drop in blood pressure, as you get vasodilatation all over, flushing of the skin and a racing heart. Lying or falling down is probably the best thing you can do.

'In addition, if you have dodgy coronary arteries, it may well trigger a heart attack. The drop in blood pressure could trigger the attack or cause arrhythmia (irregular heartbeat) in a heart that was already prone to it.'

For this reason, Dr Youlten believes there are probably a number of 'hidden' deaths attributable to stings, but which can easily be overlooked by a pathologist examining a body, unless blood tests are carried out.

'In younger people who have died, asthma has sometimes been a clear risk factor, but most children survive anaphylaxis well, even without any treatment. Some young people can have cardiac risk factors too, of course,' says Dr Youlten.

'It's well-known that the venom itself is sufficiently toxic in some cases, and that if you're frail or small, it can kill you. The other thing you can get is an infection, leading to a more prolonged problem with septicaemia in a vulnerable individual.

But although bee-keeping would seem to pose higher risks, Dr Youlten points out that the great majority of stings are from wasps.

'In fact, when you look at the statistics, wasps are far more dangerous - two thirds of deaths are due to wasps, and if you're not a beekeeper or an immediate neighbour, the chances of having a bee sting, let alone dying from a bee sting, are minimal.'

Middle-aged people seem to be more at risk of having an allergy to bee or wasp venom, says Dr Youlten. A study he made of deaths over 10 years showed that only two out of 80 deaths were of people aged under 30. Most were in their forties and fifties.

Bees and wasps seem to be attracted to people with certain types of pheromones (molecules of scent secreted by humans and animals in response to certain emotions), says Dr Youlten, and they also seem to attack people wearing dark clothes more frequently than others.

Patients referred to the clinic are given a skin-prick test to assess the severity of their allergy and are then started on a course of venom injections, with doses increasing gradually from week to week.

They are kept under observation for an hour to check whether they have an adverse reaction to the injection, and are then allowed to go home. Patients also keep a record of any side-effects and these are assessed at regular intervals.

'When patients are first referred to us, if it sounds as though they have a worrying generalised reaction, we suggest that the GP provides them with an adrenalin syringe or an adrenalin inhaler, which they carry with them all the time,' says Dr Youlten.

A controversy erupted recently when the pharmaceutical company Boots applied for a licence to import EpiPen, an adrenalin syringe, from the United States. The government's Medicines Control Agency refused the company a licence on the grounds that an alternative, Min-I-Jet, was already available. Critics say that the EpiPen can be kept for up to two years while the Min-I-Jet can be kept for only one and that EpiPen is ready-loaded with the correct dose, while the other has to be loaded by hand.

Meanwhile, the 7,000 adults and children in Britain who have allergies to bee and wasp venom, as well as to peanuts and other foods, have to hope that someone will give them adrenalin quickly enough if they have a severe reaction.