Campaigners trying to block the airport’s expansion, including a group of councils, environmental charities and Mayor of London Sadiq Khan, are bringing a legal challenge over the Government’s approval of controversial plans for the extra runway.

The case is being brought against the Government by local authorities in London affected by the expansion, Mr Khan, and charities including Greenpeace, Friends of the Earth and Plan B.

Lawyers for the campaigners told a hearing in London on Thursday that, when considering the proposals, the then transport secretary Chris Grayling did not take enough account of environmental legislation or of climate change issues.

David Wolfe QC, representing Friends of the Earth, told the court: “No-one can be unaware of the urgent need to tackle climate change.”

The barrister said that in light of the fact aviation accounts for 25% of the UK’s carbon emissions, “particular vigilance” was needed, and the charity’s focus is to ensure such vigilance is given throughout the planning process.

Nigel Pleming QC, on behalf of the councils, Mr Khan and Greenpeace, said: “The scheme will have widespread environmental consequences in terms of noise, harm to protected sites, air quality and climate change, with consequential health effects for a huge number of people.”

Mr Pleming argued the Government’s decision to approve the plans for a third runway should be quashed.

At the outset of the hearing Lord Justice Lindblom, who is hearing the case over six days with Lord Justice Singh and Lord Justice Haddon-Cave, said the issues raised are “of obvious importance”.

He said: “They will be of interest to a national and also an international audience.”

The judge added that the court will consider the legal issues only, adding: “We are not concerned with the political or other merits of the decisions under challenge.”

The campaigners are appealing against a High Court ruling in May, which rejected four separate judicial reviews of the Government’s decision to approve the plans.

They say the Government’s National Policy Statement (NPS) setting out its support for the project failed to properly deal with the impact on air quality, climate change, noise and congestion.

Government lawyers are urging the judges to reject the appeals, arguing that the High Court reached the correct conclusion.

The appeals are being heard alongside a separate challenge by Heathrow Hub, a consortium with a rival proposal for the airport’s expansion.

Jenny Bates, campaigner at Friends of the Earth, said: “Declaring a climate emergency while backing Heathrow’s third runway project shows the climate hypocrisy of our Government.

“Expanding Heathrow would lead to a huge increase in climate-wrecking emissions.

“It’s time the Government is held to account over the third runway, and for it to give some actual thought into what a third runway would mean for the planet.

“We need to be cutting down the number of planes in our skies, not giving them a massive daily boost.”

John Sauven, executive director of Greenpeace UK, said: “The ongoing air pollution crisis, and the thousands of deaths it causes, the stress and ill health from the sound of constant overflights and the destruction of communities around Heathrow all make a third runway unacceptable.

“But it’s the climate emergency which makes the third runway truly absurd.

“Our legally-binding 2050 net zero target means that we cannot continue with business as usual.

“Massively expanding aviation makes no sense. The ship of state needs to change course before we waste many millions more on this climate-changing folly.”

Tim Crosland, director of Plan B, said: “A policy to expand aviation in the midst of the climate and ecological emergency is a policy to reduce the life chances of the most vulnerable to maximise the temporary convenience of the few.”

Paul McGuinness, chairman of the No 3rd Runway Coalition, said: “If the unavoidable increases in noise pollution and poorer air quality were not enough, the recent inclusion of a net zero carbon target in the Climate Change Act has tightened the noose around Heathrow expansion even further.

“The Committee on Climate Change has highlighted that demand for aviation must be limited and that a third runway at Heathrow would inevitably mean restrictions on capacity at other airports across the UK.

“It’s now vital for Government to pause plans for Heathrow expansion, to reassess airport capacity strategy for the whole country.”

Support from Labour MPs helped push through the proposals to expand Europe’s busiest airport with an overwhelming majority of 296 in a Commons vote in June last year.

Mr Grayling said at the time that the new runway would set a “clear path to our future as a global nation in the post-Brexit world”.

Construction could begin in 2021, with the third runway operational by 2026.