An alert was issued today about London’s air quality as a toxic cloud from the Continent drifts towards the capital.

Official air quality data reveals that Greater London has already had seven days this year where air pollution was given the worst possible rating.

The system uses an air pollution scale of one to 10, with 10 being the worst and seven or over counting as high. Greater London has had seven days in 2015 with a 10 rating.

Nowhere else in the country, including other major cities such as Greater Manchester, Cardiff, Liverpool and Glasgow, has had a 10 rating so far this year.

The index works by measuring the concentration of several harmful gases and particles in the air we breathe. These include tiny PM 10 and PM 2.5 particles, which can get deep into the body.

A study published in the Journal of Environmental Protection last year found “strong evidence” that long-term exposure to air contaminated with high concentrations of tiny PM 2.5 particles can lead to a higher chance of dying from lung cancer.

Chief executive of Asthma UK Kay Boycott said: “Two thirds of people with asthma find that air pollution makes their asthma worse, putting them at an increased risk of a potentially fatal asthma attack.

“When air pollution is high it’s vital people with respiratory conditions including asthma check air pollution forecasts, carry their reliever inhaler with them at all times, and ensure that they are taking their preventer inhaler every day because this will help build resilience to asthma triggers like air pollution.”

The cloudy weather is likely to impact observations of Friday’s solar eclipse. Met Office spokeswoman Nicky Maxey said: “It is fairly cloudy tomorrow, but there is a possibility that there might be some breaks in the cloud, but it is not really possible to say where. However, most people should still be able to experience it becoming dark.”

Days with highly polluted air in Greater London since January 1 (10 = very bad, 7 =high)

  • January 27: 10
  • January 28: 10
  • February 4: 10
  • February 9: 10
  • February 10: 10
  • February 13: 7
  • February 25: 10
  • March 17: 10
  • March 18: 7

Source: Trinity Mirror Data Unit