Some 85 per cent of Britons do not do the recommended half an hour of fitness training five times a week, according to research.

Conducted by the Stroke Association, the survey of 3,000 people also found that half of Britons eat too much salt.

The poll was released to mark the launch of a new Stroke for Stroke campaign, which aims to get people rowing 10km for charity on an indoor rowing machine.

A combination of too much salt and a lack of exercise can lead to high blood pressure, the biggest single factor in increasing the risk of a stroke, says the association.

Joe Korner, from the Stroke Association, said: "Regular exercise and lifestyle choices can help prevent a stroke - clearly a message Britain still needs to hear."

More than 150,000 people in Britain a year suffer a stroke, yet almost two-thirds of those surveyed said that they were unconcerned about how much salt they ate.

The Food Standards Agency recommends that adults limit their salt intake to just 6g, or one teaspoon, a day.