BRITAIN has been placed on a health alert because a potentially dangerous cloud of air pollution is blowing over the country.

Experts said the smog could cause fatal asthma attacks and have warned the elderly and those with health problems to be cautious.Dorset residents have been told the warning is at the moderate level.

The Department for Environment, Food and Rural Affairs (Defra), said air pollution was blowing in from Europe and mixing with home-grown smog to create the problem.

Officials warned this could trigger health difficulties for those with respiratory illnesses and the elderly, although it does not pose a health threat for the general population.

Large parts of England will see air pollution climb to moderate levels today while parts of the north will see it hit nine out of 10.

A Defra spokeswoman said: "Winds bringing in pollution from the continent, combined with locally generated pollution and still weather conditions has led to some high pollution measurements across the UK.

"Levels are expected to return to low bySaturday."

Dorset currently has moderate levels of pollution at five out of 10 on Defra's scale. This will continue into tomorrow and return to lower levels across the weekend.