Tens of thousands of lives may have been lost as a result of erroneous advice by doctors on the treatment of one of the most common medical conditions, affecting two million people in Britain. In an unprecedented move, the National Institute for Clinical Excellence (Nice), the Government's medicines watchdog, is to revise guidelines on the treatment of high blood pressure that were issued only 15 months ago.

No mechanism existed to make early revisions to Nice guidelines, which are normally reviewed every four years, until the latest evidence on the treatment of blood pressure emerged.

The error occurred because specialists made an unwarranted assumption more than a decade ago that drugs called beta blockers which worked for patients with existing heart disease would be equally effective in those with high blood pressure but without heart disease, even though they had never been tested against other drugs.

Now a review of research has shown that although beta blockers are an effective treatment for high blood pressure, they are significantly worse than other drugs at protecting sufferers from damage to their circulatory system.

The British Heart Foundation warned yesterday that patients whose blood pressure was well controlled on beta blockers should not stop taking them and should await the new advice from Nice, expected in six months.

"Stopping beta blockers could be dangerous and would be the worst thing they could do," said a spokesman.

For three decades, beta-blockers have been the gold standard treatment for high blood pressure and have been credited with saving hundreds of thousands of lives.

High blood pressure increases the risk of heart attacks and strokes.

The review of 13 randomised trials involving 105,000 people published in the current issue of The Lancet found that beta blockers reduced the risk of strokes by 19 per cent but other treatments such as diuretics, ACE inhibitors and calcium channel blockers reduced the risk by 38 per cent.

The overall death rate among those on beta blockers was 3 per cent higher. All the drugs are available in cheap generic form so switching would not add to costs, the researchers said.

Beta blockers were originally prescribed as a treatment for heart disease but doctors argued that as they were so effective, their use should be extended to first-line treatment of ordinary high blood pressure.

Professor Lars Lindholm of the University of Umea in Sweden, who led the study, said "That was the mistake. The step we took from secondary prevention to primary prevention just didn't work. Beta blockers are fantastic drugs for heart disease. But although they work for hypertension [high blood pressure] they are only about half as effective as other drugs."

He added: "It was a very honest mistake. Back in the 1960s when beta blockers were discovered, it was such a relief that we could treat our patients. The difference was so impressive, we were overjoyed."

Professor Peter Weissberg, the medical director of the British Heart Foundation, said the changing perception of beta blockers reflected the natural evolution of medicine, beginning with the discovery that blood pressure could be reduced by drugs followed by "fine tuning" to decide which drug was best.

However, blood pressure drugs have been available for decades and the evidence on which is most effective has only emerged by chance in the past year.

Professor Weissberg said: "When you have relatively cheap [generic] drugs no one is going to go out and fund an expensive trial to find out if one works better than the other."

Professor Bryan Williams, chairman of the British Hypertension Society's NHS guideline development group, which will lead the review of the Nice advice, said: "The problem is that people looked at beta blockers and other drugs as interchangeable. The head-to-head trials were not done.

"We are talking here about treating millions of people. If we are going to start population treatment strategies then the treatments we use should be vigorously tested."