Boris Johnson is facing calls from the Green Party to tackle air pollution in the capital.

It comes on a day in which DEFRA warned that high levels of pollution had been recorded in rural areas of south-east England and people with health problems living should take care.

Jenny Jones, Green Party member of the London Assembly, said the Mayor of London now need to "think big" to help Londoners avoid the health risks associated with air pollution.

She said: "The Mayor is sitting idly by while millions of Londoners are exposed to pollution that can permanently damage their health. He is telling the vulnerable to avoid outdoors exercise, but does virtually nothing about the cars and lorries that cause the pollution. The Mayor stripped out the type of emergency measures that could have restricted traffic during periods of smog from his air quality strategy.

"Rather than solving the problem the Mayor seems intent on making the problems worse, backing new road building schemes and increased airport capacity.”

Defra (the Department for Environment, Food & Rural Affairs) has a 10-point scale for measuring air quality - with level one implying a "low" risk of air pollution and 10 for "very high" levels. It said some areas of the UK could reach "very high" levels of air pollution later and elderly people and those with lung or heart disease should not exercise outside.

The Liberal Democrats' environment spokesman at the London Assembly, Stephen Knight, said schools located near pollution hotspots and busy roads needed more support to protect children.

He said: "We should never forget that children are at great risk from air pollution because of their smaller lung capacity, and their height which means that they are often closer than adults to tail pipe exhaust emissions from vehicles.

“Of course there are numerous reasons for the current levels of high pollution, including dust being blown over from the Sahara, but the harsh reality is that these week’s exceptional factors are just exacerbating daily problem of high levels of pollution that exist everyday in many parts of London.”

Mr Knight said a survey of 935 London schools and nurseries that are situated within 150 metres of a major road revealed just two per cent of schools were aware of the airTEXT service which provides free daily air pollution forecasts for Greater London. The results also suggest a lack of awareness of the information and support services available through the Mayor's Cleaner Air 4 Schools education programme.

The Lib Dem spokesman added: "At present only feeble steps are being taken by the Mayor to inform Londoners about air pollution. The Mayor's claim that the airTEXT provides an adequate service to help vulnerable Londoners is totally demolished by the results of this survey."