A high air pollution alert has been announced amid an “air quality crisis” in the capital.

This is the 10th time the air pollution alert system has been used since Sadiq Khan became the Mayor of London in 2016 – once for ‘very high’ air pollution levels and nine times for ‘high’ pollution levels.

A spokesperson for the Mr Khan said: “The high levels of pollution expected over the next few days is evidence of the scale of London’s air quality crisis and is exactly why the Mayor is taking hard-hitting measures to clean it up.”

Mr Khan said the launch of the Ultra Low Emissions Zone (ULEZ) in central London is expected to reduce harmful emissions in the zone by around 45 per cent. He has also launched a diesel scrappage scheme for small businesses to scrap polluting vehicles.

This particular episode of high air pollution levels is due to poorly dispersed emissions and air pollution particles which have travelled to the UK from Europe, although pollution levels are highest next to busy roads.

Signs alerting people to air pollution levels will be placed by London Underground stations, on roadsides and by river pier sounds.

The Government’s Committee on the Medical Effects of Air Pollutants (COMEAP) has advised people with lung problems too reduce physical activity, particularly outdoors.

The last recorded high pollution in London was on July 25, 2018.