But today Heathrow Airport Limited vowed to take the case to the Supreme Court saying that environmental concerns could easily be rectified.
Judges this morning ruled that ministers had not done enough to tackle climate concerns when they gave it the green light.
The unlawful ruling raises the prospect that the Prime Minister, who has previously argued against airport expansion, could pull Government support for the £14bn scheme, which is largely to be funded by the private sector.
Lord Justice Lindblom told the court: “The Paris Agreement ought to have been taken into account by the Secretary of State in the preparation of the NPS and an explanation given as to how it was taken into account, but it was not.”
But the judges said that in future, a third runway could go ahead, as long as it fits with the UK’s climate commitments.
A Heathrow spokesperson said: “The Court of Appeal dismissed all appeals against the government – including on “noise” and “air quality” – apart from one which is eminently fixable. We will appeal to the Supreme Court on this one issue and are confident that we will be successful.
“In the meantime, we are ready to work with the Government to fix the issue that the court has raised.
“Expanding Heathrow, Britain’s biggest port and only hub, is essential to achieving the Prime Minister’s vision of Global Britain.
“We will get it done the right way, without jeopardising the planet’s future. Let’s get Heathrow done.”
Campaigners fighting to stop the expansion of Heathrow first failed in their attempt to block the new runway in the High Court last year, but decided to appeal the decision.
The case was brought by local authorities, Greenpeace, Friends Of The Earth and rival extended runway scheme Heathrow Hub.
They argued that the government’s National Policy Statement, setting out its support for the project, failed to account fully for the impact on air quality, climate change, noise and congestion.
Developer of the rival Heathrow expansion plan, Arora, said its Heathrow West plan could be the quicker, better and greener solution that allows the third runway to happen as it better solves the environmental and cost problems but adds the same capacity.
An Arora spokesperson said: “The Arora Group remains an unwavering supporter of Heathrow Expansion so long as environmental disruption is minimised. Expansion’s impact on our country’s infrastructure is unparalleled and will considerably benefit every region of the UK.
“We believe our own plans to design, develop and operate Heathrow West – a new terminal servicing the new runway – will revolutionise the airport and ensure an expanded Heathrow is efficient and cost-effective versus the expensive and inefficient plans put forward by Heathrow Airport Limited.
“Crucially, with the ability to deliver the fully expanded airport 18 years earlier than HAL and in requiring significantly less land take, the environmental impact of our plans will be streets ahead.”