Asthma could be cured within five years after scientists discovered what causes the condition and how to switch it off.

In a breakthrough which could change the lives of Britain’s five million sufferers, researchers at Cardiff University and Kings College London identified which cells cause the airways to narrow when triggered by irritants like pollution.

Crucially, drugs already exist which can deactivate the cells. They are known as calcilytics and are used to treat people with osteoporosis.

The scientists are hopeful that in the future asthmatics take the drug to prevent an attack ever happening and ending the need to constantly carry an inhaler.

"Our findings are incredibly exciting," said Professor Daniela Riccardi, from Cardiff University School of Biosciences.

"If we can prove that calcilytics are safe when administered directly to the lung in people, then in five years we could be in a position to treat patients and potentially stop asthma from happening in the first place.”

Asthma is a debilitating long-term condition which can cause coughing, wheezing, chest tightness and breathlessness. Although inhalers can manage the problem, some people do not respond to current treatments.

Scientists knew that asthma was caused by inflammation in the small tubes which carry air and out of the lungs, but did not know what was triggering it.