Young children could be given a vaccine or treatment which would prevent asthma and other serious diseases such as rheumatoid arthritis within the decade, scientists believe.

The optimistic prediction is based on a growing consensus among medical researchers that allergic types of asthma and apparently unrelated diseases such as rheumatoid arthritis could have a common biological cause. Experts in Aberdeen and London believe that problems with the same cells which are crucial to controlling the body's immune system, which are known as T regulatory cells, are to blame for causing both these forms of disease.

Until recently, immunologists believed the two types of disease, known as allergic and auto-immune diseases, had different biological mechanisms. The latest hypothesis has contradicted that idea.

Although at an early stage, the new theory suggests scientists are close to finding the environmental and biological cause for these diseases, and to developing treatments using vaccines based on harmless bacteria, gene therapies or environmental changes.

Professor Martin Partridge, chairman of the National Asthma Campaign and of the British Thoracic Society, added: "This hypothesis is probably the most credible explanation we've got for the increase in the prevalence of allergic diseases."

That could also provide a sliver of hope for diabetics suffering from Type 1 diabetes, which is also believed by some experts to be an auto-immune disease. Experts on diabetes are extremely cautious about the prospects of a cure but, if proven, immunologists suspect the treatment for allergies could be useful for Type 1 diabetes.

The hypothesis adds greater credibility to the belief that modern lifestyles could be the cause of parallel increases in diseases such as asthma and auto-immune diseases in Western countries. Immunologists believe that a lack of exposure to once common infections in infancy has meant children's immune systems are less able to prevent diseases such as asthma. Poor diets and pollution could be the trigger for these diseases.

About 5.8 million Britons suffer from allergic diseases such as asthma, and millions more from hay-fever and eczema. Auto-immune diseases include rheumatoid arthritis, of which there are 387,000 sufferers.

Dr Robert Barker, an immunologist at the University of Aberdeen, presented the hypothesis at a Royal Society of Edinburgh seminar on asthma earlier this month. "If we can understand how environmental factors interact with the immune system, it's possible we may be able to design some therapy to break the link between these factors and the immune system," he said.

Dr Aziz Sheikh, a National Health Service research fellow at Imperial College, said this explanation suggested that within the next seven to eight years, a bacteria-based vaccine or a form of immune therapy will be found which will prevent all these diseases.

It would increase pressure on the Department of Health and funding bodies such as the Medical Research Council to step up spending on basic research, he added. "There are possibilities for reversing this epidemic, possibly by giving some harmless bacteria early on in life," he said.