Researchers have found for the first time a key step in how the body controls blood pressure and so how the process sometimes goes wrong.

By targeting the mechanism they can stop it from malfunctioning and so prevent the condition, known as hypertension, that affects millions of people in Britain and is a major cause of heart disease and stroke.

The researchers at Cambridge University and Nottingham University discovered the mechanism while studying pre-eclampsia, a potentially

deadly form of high blood pressure which occurs in women during pregnancy. Blood pressure is controlled by hormones called angiotensins which in too high a dose forces blood vessels to contrict, increasing blood pressure.

The scientists, who have spent 20 years researching the hormones, have discovered the very first stage in their development. They now believe they could develop a way of inhibiting the "switch" that allows the hormones to overproduce and prevent the onset of high blood pressure.

Professor Robin Carrell at the University of Cambridge, said: "We have found the first step in the main process that controls blood pressure.

"We are excited by what we have found because of the potential insights it provides us. Knowledge of what causes a disease is the number one factor needed for its eventual management and treatment.

"By getting a step earlier and looking at an earlier change we are opening up new strategies and coming closer to the reason why some people develop hypertension."

Dr Aiwu Zhou, a British Heart Foundation (BHF) Fellow at the University of Cambridge, said: "Although we primarily focused on pre-eclampsia, the research also opens new leads for future research into the causes of hypertension in general."

Millions of people in Britain suffer from hypertension, one of the major causes of heart disease and stroke and drugs that treat it make up six per cent of all prescriptions.

Drugs currently used to treat high blood pressure – such as ACE inhibitors – focus on the later stages of the mechanism that controls blood pressure.

The study, which was published in Nature, hopes to lead to new inhibitors that nip the condition in the bud before it has caused any damage.

High blood pressure frequently affects pregnancy. However, in two to seven per cent of pregnancies this develops into pre-eclampsia, which threatens the health and survival of both the mother and child.