Heathrow airport’s plans to build a third runway were dealt a crushing blow after the UK government said it would not appeal against a court ruling that the £14bn project was unlawful on environmental grounds.

The judgment delivered by the Court of Appeal found that the government had failed to take into account commitments made under the 2016 Paris agreement on climate change when assessing Heathrow’s expansion plan. It ruled that this made the government’s airports policy unlawful.

The ruling is a serious setback for Heathrow in its long-running effort to build a third runway, which has dragged on for more than a decade. The airport will launch an appeal against the decision at the Supreme Court.

Ministers declined to give even lukewarm support to the project on Thursday, saying they would not spend taxpayers’ money on a government appeal.

Boris Johnson, who represents the nearby seat of Uxbridge, had previously vowed — as a backbench MP — to “lie in front of the bulldozers” to block the third runway.

The court decision has potentially removed a thorny political dilemma for the prime minister. “This is a Pontius Pilate moment for Boris, because it lands a potentially killer punch to Heathrow but the PM can say ‘it’s nothing to do with me’,” said one Tory MP.

Yet Grant Shapps, transport secretary, said the government had not given up on the idea of improving aviation capacity either at Heathrow or elsewhere as the industry became more “sustainable” in the future.

“Airport expansion is core to boosting global connectivity,” he said. “We also take seriously our commitment to the environment.” Mr Shapps said that the expansion was now up to the industry: “What happens next will be up to Heathrow.”

One official said that the government had not sounded the “death knell” for the project. Instead it was merely giving “less full-throated support for the single option of Heathrow”.

Lord Justices Lindblom, Singh and Haddon-Cave handed down their ruling to a packed courtroom that erupted into jubilation after the decision. Campaigners crowded outside the doors called it a “historic” and “amazing” day.

“We face a climate emergency and I’m delighted that the Court of Appeal has recognised that the government cannot ignore its climate change responsibilities,” said Sadiq Khan, London’s mayor, who was involved in one of the judicial reviews.

“The government must now finally see sense and abandon plans for a third runway at Heathrow.”

Crucial to the judges’ decision was erroneous legal advice given to Chris Grayling, the former transport secretary, who was told not to take the Paris Agreement into account when drawing up the airports national policy statement. The ANPS, which was backed by MPs in 2018, cleared the way for Heathrow expansion.

The judgment noted, however, that a third runway could still go ahead — even if Heathrow loses its appeal — but only if the government rewrote its airport policy statement in line with the UK’s climate commitments.

A Heathrow spokesperson said it believed the ruling was “eminently fixable”, adding that it was “ready to work with the government to fix the issue that the court has raised”.

But that would depend on Mr Johnson authorising an overhaul of the ANPS to approve a scheme that he has long opposed.

An official said no decision had yet been taken about whether the government would seek to rewrite the document. “There are lots of different options,” he said.

The need for more capacity at Heathrow dates back to the 1960s but attempts to build a third runway began in earnest early in the past decade. The former Labour government backed the project but it was cancelled in May 2010 by the incoming Tory-Liberal Democrat coalition. In 2015, the independent Airport Commission backed the scheme and it became the official policy of the subsequent Conservative government in 2016.

Andrew Adonis, the former transport secretary in the last Labour government, criticised the Court of Appeal ruling. “The only winners from a refusal to expand Heathrow as agreed by parliament two years ago will be other international hubs that will take the extra traffic, especially Amsterdam, Paris and Dubai,” he said. “There won’t be fewer flights, they just won’t come to Britain.”

Business groups also criticised the ruling, warning that without Heathrow expansion companies risked losing regional connectivity and access to markets around the world.

Adam Marshall, director-general of the British Chambers of Commerce, said: “There has never been a more important time to demonstrate that Britain is open for business. The government must back Heathrow expansion unequivocally and take all necessary steps to finally move the project forward.”

Margaretha Wewerinke, assistant professor of public international law at Leiden University, said the decision could have “global” implications.

“For the first time, a court has confirmed that the Paris Agreement temperature goal of pursuing efforts to keep warming below 1.5C has binding effect,” she said, adding that it could “inspire similar litigation in other countries that have signed the Paris Agreement”.

Letter in response to this article:

A sight I had longed to see / From Peter Bloxham, London WC2, UK

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