London pollution alert issued over 'toxic air'

London’s nine million inhabitants have been urged to avoid unnecessary car journeys to combat the “toxic air” circulating in the city as part of the first major warning over pollution in two years.

Sadiq Khan, the mayor of the UK capital, issued the alert, asking Londoners to walk, cycle or use public transport rather than use private vehicles. Drivers should also refrain from idling with their engines on and people should not burn wood or garden waste, he said.

“Toxic air is dangerous, particularly for those with heart and lung problems,” Mr Khan tweeted.

“A high pollution episode is forecast from now to Thursday. Please look after each other by walking, cycling, avoiding unnecessary car trips, stopping engine idling and not burning wood or garden waste.”

The alert issued on Tuesday is set to expire on Thursday. It was triggered by an Imperial College London forecast that imported pollution will add to a build-up of domestic emissions, Mr Khan’s office said in a statement.

Pollution remains a grave problem in the city and poor air quality is associated with 4,000 premature deaths a year, according to city officials.

According to the World Air Quality Index Project, central London on Thursday afternoon recorded a reading of 149, which is "unhealthy for sensitive groups".

London's Ultra-Low Emission Zone, which covers areas within the North and South Circular Roads, was introduced to lower the capital’s pollution rates. It requires the drivers of vehicles which do not meet ULEZ emissions standards to pay a £12.50 daily charge to drive inside the zone.

The zone will next year be expanded to cover an area of more than 600 square miles.

London’s measured levels of PM2.5, an air pollutant that is a concern for people’s health when levels are high, stands at more than eight times above guidelines issued by the World Health Organisation, according to IQAir, a Swiss company that makes air quality monitors and air purification technologies.

Hundreds of millions of people globally are being affected by dirty air that far exceeds health standards, the firm said in a report published on Tuesday.

A report by Inrix, a US-based analytics company, last year named London as the world’s most congested city.

Mr Khan has previously said people living in London face a crisis of “filthy air and gridlocked roads” unless the use of cars is reduced.