The nasal spray stops blood vessels from becoming inflamed by helping the body counter the protein responsible.

However, stroke experts have warned that it may be more effective simply to improve patients' lifestyle.

People with long-term high blood pressure are more likely to suffer a stroke - and develop heart disease - as the walls of their blood vessels become damaged.

The latest vaccine helps the body target a protein called E-selectin which is key to a process by which the blood vessel walls become inflamed.

It is hoped that it may trigger the release of body chemicals which damp down this inflammatory reaction.

Stroke is a leading cause of death in the UK, and happens when a blood clot lodges in a blood vessel supplying the brain.

The blockage starves part of the brain of oxygen-rich blood, and causes brain cells to die.

This damage can cause long-lasting disability, or even kill the sufferer.

Stroke rats

The latest research involved giving a strain of stroke-prone rats with naturally high blood pressure doses of E-selectin, to try to prime the body to react to it.

Those given the longest course of vaccine had 16 times fewer strokes caused by blood clots than those given a fake "control" vaccine.

None of those given the longest courses suffered a haemorrhagic stroke, in which a burst blood vessel in the brain causes similar damage.

Scientists believe that priming the system with E-selectin encourages a type of blood cell called a lymphocyte to release inflammation calming factors when they meet it routinely.

Cutting the inflammation may help reduce the long-term damage caused by the high blood pressure, even though the vaccine had no effect whatsoever on the blood pressure itself.

Healthy living

However, a spokesman for the Stroke Association said there were established methods of protecting the body from high blood pressure and stroke.

She said: "This research has proved some interesting results, and will be of benefit to those who suffer from high blood pressure.

"We look forward to seeing further results once the trials begin.

"We know that high blood pressure is a risk factor for stroke, in fact, four in 10 people could have prevented their stroke if they had had their blood pressure checked and monitored.

"Simple lifestyle changes can help to reduce high blood pressure and subsequently stroke such as eating a healthy diet, taking more exercise, giving up smoking and drinking sensibly."