The Seretide inhaler has been described as "an evolutionary milestone" in asthma care.

Professor Peter Barnes: "Inhaler should give much better control of symptoms."

Manufacturers Glaxo Wellcome claim the new inhaler will improve the breathing of asthmatics, reduce wheezing and reduce the need to rely on 'blue' reliever inhalers.

The treatment is not designed to treat serious bouts of asthma, but trials have shown that patients who take the new treatment on a regular basis have experienced a marked reduction in both minor and severe attacks requiring hospitalisation.

Until now, asthma sufferers have had to use two inhalers, one to control the inflammation that causes the condition, and one to protect them against asthma symptoms.

Professor Peter Barnes, an asthma expert at the Royal Brompton Hospital, London, said: "Seretide is an evolutionary milestone in the treatment of asthma.

"It will help to ensure that patients receive the important therapies that they need to keep their asthma under control in one convenient inhaler."

Many sufferers do not take their 'brown' preventer inhaler (inhaled steroid) as often as they should because they do not feel better immediately.

Glaxo Wellcome says that patients taking Seretide should feel the benefits of improved breathing from the first day of treatment, which may encourage them to continue to take their important preventer treatment on a regular basis.

Seretide is available in three strengths, Seretide 100, Seretide 250, and Seretide 500, which means that doctors can choose the right inhaler for every patient's needs.

Clinical studies in over 2,700 patients have shown that Seretide is a highly effective and well-tolerated treatment in controlling asthma.

Professor Barnes said nobody knew why asthma was on the increase.

He said: "There is much more asthma about, and this is something that is happening in every country.

"We don't exactly know the reasons why, but is something that is linked to western civilisation.

"There are many people with asthma that are still under-treated, and this sort of new advance in management will help to improve the over-all treatment.".

Dr Martyn Partridge, chief medical advisor to the National Asthma Campaign, welcomed the launch of Seretide.

But he said people who were currently taking separate reliever and preventer medications should discuss whether to switch with their GP as the doses they received from Seretide may be different.