Doctors are today being warned that occasional high blood pressure readings could be a signal that a patient is at risk of stroke.

Researchers say variations in blood pressure can also indicate an increased risk of angina, heart attacks and heart failure.

The findings are expected to lead to new recommendations in the way doctors treat patients.

Lead researcher Professor Peter Rothwell said: "Previously, such fluctuations were considered to be benign and uninformative.

"We have shown that it is variations in people's blood pressure rather than the average level that predicts stroke most powerfully.

"Occasional high values, and what might be called episodic hypertension, carry a high risk of stroke."

He added that patients who have normal blood pressure readings with occasional spikes should be treated with blood pressure lowering drugs.

Such drugs are among the most frequently prescribed on the NHS, with more than 15 million in people being treated for high blood pressure.

Professor Rothwell said: "The work shows that many patients need blood-pressure-stabilising drugs – a new concept – as well as blood-pressure-lowering drugs."

Prof Peter Weissberg, from the British Heart Foundation added: "High blood pressure is extremely common, and an important risk factor for heart attack and stroke. These researchers suggest that measuring blood pressure variability – rather than single recordings of blood pressure – may be important.

"Current practice is not wrong, but this might add a new measure to help doctors make decisions on who to treat for hypertension and which drug to use.

"People taking beta blockers should not be alarmed or stop their treatment suddenly, which can be dangerous. There are several potentially life-saving reasons to give someone a beta blocker. Those with concerns should talk to their GP."

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