Drivers should “think long and hard” before buying a diesel car and instead consider purchasing a low-emission vehicle, the transport secretary has said, as the government considers a strategy to tackle air pollution.

Chris Grayling’s intervention took place as the Guardian revealed that tens of thousands of London’s children were attending schools in areas with levels of toxic air in breach of EU legal limits. The minister also said the government had a legal duty to cut emissions of nitrogen oxide from diesel cars, which account for four in 10 vehicles on British roads, after a high court ruling in November ordered the authorities to reduce levels of the toxic fume in the “shortest possible time”.

Speaking to Saturday’s Daily Mail, he said: “People should take a long, hard think about what they need, about where they’re going to be driving and should make best endeavours to buy the least polluting vehicle they can.

“I don’t think diesel is going to disappear but someone who is buying a car to drive around a busy city may think about buying a low-emission vehicle rather than a diesel.”

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No 10 is also understood to be considering a scrappage scheme for diesel cars that would see drivers offered a cash incentive for replacing an old diesel car with a low-emission alternative in a bid to improve the country’s air quality.

It is expected to publish an official strategy in the coming weeks.

Last week London’s mayor, Sadiq Khan, announced plans to introduce a £10-a-day “toxicity charge” on older, polluting cars entering central London on weekdays from October this year. Speaking about the forthcoming T-charge, Khan said: “It’s staggering that we live in a city where the air is so toxic that many of our children are growing up with lung problems. If we don’t make drastic changes now we won’t be protecting the health of our families in the future.”

Concerns over the impact of diesel cars on nitrogen oxide levels were highlighted during the Volkswagen emissions scandal in September 2015 after it emerged that 11m of the German car giant’s diesel vehicles had been fitted with software to release fewer smog-causing pollutants during tests compared to real-world driving conditions.

A government report published in April 2016 showed that diesel cars being sold in the UK emit an average of six times more nitrogen oxide in real-world driving conditions than the legal limit used in official tests. The Department for Transport investigation found all of the 37 top-selling diesel cars tested exceed the legal limit required for laboratory tests when driven for 90 minutes on normal roads. Ministers insisted no laws had been broken by the manufacturers as cars are only required to meet the lab test regulations. Analysis by the Department for Environment, Food and Rural Affairs found that nitrogen oxide is estimated to be responsible for 23,500 deaths in the UK each year while the Royal College of Physicians and of Paediatrics and Child Health warned last year that the figure was closer to 40,000.