Proposals to redefine “high blood pressure” and offer more patients medication could increase the risk of the condition, a new report suggests.

The National Institute for Health and Care Excellence (Nice) is currently considering evidence which has led the US to change its advice, making millions more patients eligible for daily drugs to cut their heart attack risk.

The criteria could mean almost half of Britons become eligible for drugs to reduce their blood pressure.

But a report by the University of Sydney says such changes could put lives at risk - partly because a diagnosis of high blood pressure is likely to increase anxiety levels. Episodes of anxiety and stress can cause spikes in blood pressure.

Other patients could see an increased risk from side-effects of medication, without a reduction in their risk of heart disease, their findings suggest.

Currently, around seven million Britons whose blood pressure exceeds 140/90 are recommended to take blood pressure pills, with higher limits set for patients over 80.

The drugs, which cost the NHS as little as 10 pence a day, are normally recommended for patients deemed to have a 20 per cent risk of heart disease or stroke within the decade.

But the guidelines published by the American Heart Association bring the systolic threshold down to 130/80 - which is estimated to mean a 10 per cent chance over the same period.