An independent report commissioned by the Government contradicts its claim that the planned third runway at Heathrow will not affect the UK’s efforts to bring air quality into line with legal safety limits.

In the latest episode of the tragedy of errors surrounding the Government’s attempts to keep air pollution within acceptable standards, Transport Minister Chris Grayling proudly announced “we will meet our legal requirements on air quality” and fossil fuel emissions despite the airport expansion.

However, as he spoke, the Department for Transport released an analysis by consultants WSP Parsons Brinckerhoff.

And it said: “There is a risk that the [extra runway] options will delay or worsen compliance with limit values.

“This risk is lowest for Gatwick 2R [Second Runway] and highest for the Heathrow options, in particular Heathrow ENR [extended northern runway] without the updated surface access strategy in place.

“Furthermore, the risk increases the earlier the option is assumed to come into operation.”

However the consultants added the extra runway would eventually come into line with European Union air quality regulations, saying it would “not affect compliance” in 2030.

Their report laid out the Government’s embarrassing record on air pollution in stark detail.

In 2015, the Airports Commission had been asked to look into the effect of the third runway based on the Ministers’ then plan to bring the UK into line with EU rules by 2030.

But the Government was successfully sued by legal environmental activists ClientEarth over this lengthy delay with the Supreme Court ordering it to come up with a new, more effective plan.

This document was published in December 2015 with a revised target of 2025.

ClientEarth went back to court and, once again, judges ordered the Government to come up with a better plan.

This is now due to be published by the end of July this year.

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Despite the lack of the new improved target, the Government’s policy document on Heathrow expansion stated that Ministers believed “the Heathrow Northwest Runway scheme would be capable of being delivered without impacting the UK’s compliance with air quality limit values”.

John Sauven, executive director of Greenpeace UK, which first spotted the contrasting assessments, said: “Now we have it straight from the horse’s mouth.

“The Government-commissioned assessment shows a third runway risks delaying action to bring air pollution down to legal levels for years.

“And even after 2030, ministers’ hopes of complying with air quality laws are based on drivers using less polluting cars.

“But with an air pollution crisis already linked to over 9,000 premature deaths a year in London alone, people’s health cannot be dependent on rose-tinted assumptions and a notoriously unreliable car industry.

“It’s time for ministers to come clean. They don’t have a solution to the extra emissions from a third runway that will cause more air pollution and climate change. Going ahead with this project would be reckless and unlawful.”

The news comes as school governors in London have suggested that pupils should wear pollution masks while travelling to and from school.

ClientEarth’s chief executive James Thornton said: “If we have got to the point where parents are reaching for masks to protect their children’s lungs as they walk to school, it’s clear that the Government has done much too little to tackle illegal air pollution or reassure parents that they are protecting our health.

“While using masks is a proactive step by parents to safeguard children’s health, pollution must be tackled at source.

“There are just weeks to go before the Government reveals its new plans to clean up the UK’s toxic air.

“They must protect children across the country with bold measures to tackle air pollution. We need to see a comprehensive network of Clean Air Zones, targeted scrappage schemes for the dirtiest diesel vehicles and, in the short term, measures to combat pollution spikes.”

ClientEarth recently warned the Government that it could take Ministers to court again, but this time over its failure to produce a plan to cut the UK's fossil fuel emissions.