Video report by ITV News Correspondent Damon Green
Britain has been placed on a health alert as a potentially dangerous cloud of air pollution blows over the country.
Experts said the smog could cause fatal asthma attacks and warned the elderly and those with health problems to be cautious.
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 potentially toxic problem.
Officials warned this could trigger health difficulties for those most at risk, 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 highs of nine out of 10.
Kay Boycott, chief executive of Asthma UK, warned asthmatics to:
Check air pollution forecasts
Carry their reliever inhaler with them at all times
Ensure they take their preventer inhaler every day
A Met Office spokeswoman said high pressure and very few winds is causing the pollution patch to hang around.