London toxic air alert issued as Mayor Sadiq Khan warns of 'public health emergency'

People with certain health conditions urged to consider 'reducing strenuous physical activity outdoors'

A toxic air alert has been issued for London over the next three days, as Mayor Sadiq Khan warned of a "public health emergency".

Air pollution is set to hit a "high peak" in central parts of the capital including Westminster and the Square Mile, after rising to "moderate" in a total of 17 boroughs on Wednesday.

While levels of toxicity are set to return to normal on Friday, airtext forecasts issued by the Mayor suggest many of London's busiest roads will suffer "high" pollution on all three days.

Mr Khan said: “London’s dirty air is a public health emergency.

“We will continue to use all the technology at our disposal to inform Londoners about levels of air pollution in their neighbourhoods.”

Official advice issued by the Department for the Environment says: "Adults and children with lung problems, and adults with heart problems, who experience symptoms, should consider reducing strenuous physical activity, particularly outdoors."

If air pollution hits "high" levels, these groups of people are advised to reduce strenuous physical exertion, particularly outdoors, and particularly if they experience symptoms.

"Anyone experiencing discomfort such as sore eyes, cough or sore throat should consider reducing activity, particularly outdoors," the guidance says.

London Mayor Sadiq Khan (Getty)

"People with asthma may find they need to use their reliever inhaler more often. Older people should also reduce physical exertion."