Britain is on a health alert as a cloud of potentially toxic smog from the Continent threatens to smother the country within 24 hours.
Officials warned that on Thursday (March 19) air pollution could trigger deadly asthma attacks and heart problems especially in vulnerable people.
Experts said levels will be high enough to cause sore throats and itchy eyes even in otherwise healthy people.
The Department for Environment Food and Rural Affairs (DEFRA) warned parts of the north will be the worst hit, but London is also expected to be affected.
The capital is braced for moderate to high pollution levels.
The main risk is from 'particulate matter' - small particles and chemicals thrown into the air from motor vehicles and fires.
Experts said levels in London on Wednesday morning (March 18) were three-times the recommended EU limit.
A Defra spokesman said: "Adults and children with heart or lung problems are at greater risk of symptoms.
"Follow your doctor's usual advice about exercising and managing your condition.
"It is possible that very sensitive individuals may experience health effects even on low air pollution days."
Levels are expected to remain raised until the weekend thanks to a swathe of air being dragged in from Europe.
The current calm and mild weather in Britain is also fuelling the problem allowing pollution to build up especially in cities.
Pollution levels 'rocket'
A Met Office spokesman said: "Some individuals, such as those with existing heart or lung conditions, may experience increased symptoms.
"The Met Office is working very closely with Defra and Public Health England (PHE) to ensure they have the most up-to-date and accurate air quality forecasts in order to provide relevant advice to the public."
Chris Burton, forecaster for The Weather Network, said: "A combination of light winds and a slight breeze off the near Continent has led to pollution levels rocketing across parts of the UK.
"High pressure is sat right on top of the UK, preventing pollution from dispersing and keeping it trapped at the surface.
"Pollution levels are expected to be moderate or high across much of England and Wales through Thursday, with parts of eastern Scotland also elevated levels of pollution.
"Particulate matter is the main concern with levels well above recommended levels.
"On Wednesday morning, London had some of the highest levels with PM2.5 levels nearly three-times above the EU recommended limit."
A similar spike in pollution last spring led to emergency services reporting a rise in call outs to patients with respiratory issues.
Experts said pollutions levels should have dropped off enough in time for Friday's partial solar eclipse.
Originally published on Mirror Online.