Heathrow Airport's plans for a third runway have been defeated in a landmark Court of Appeal ruling.

The court issued a historic judgement against the £14billion expansion plans for Britain's busiest airport - in a massive victory for green groups and London mayor Sadiq Khan .

Three top judges said the National Policy Statement - the government's document which gave the runway the green light - was drawn up unlawfully because bungling Transport Secretary Chris Grayling didn't take into account the Paris Agreement on climate change.

The UN's Paris Agreement, which came into force in November 2016, commits signatories to tackling climate change by taking measures to limit global warming to well below 2C.

The Court of Appeal ordered that the NPS is dropped and rewritten. Lord Justice Lindblom told a packed court the government can still bring back a new NPS allowing a third runway - if it wants.

But crucially the government - whose Prime Minister Boris Johnson vowed to stop the runway by laying down in front of the bulldozers - has not asked for permission to appeal to the Supreme Court.

Undated handout image issued by Heathrow Airport of an artist's impression showing how Heathrow Airport could look with a third runway
The airport's operators had hoped to open a £14bn third runway by 2026

Today's ruling will pile pressure on Boris Johnson to keep his pledge to stop the airport's expansion once and for all after he spent years avoiding scrutiny on the subject.  

Heathrow Airport had hoped to build a privately-funded third runway by 2026 - and after years of delays MPs backed it 415-119 in 2018.

But those plans are now hurled into chaos.

Lord Justice Lindblom stressed: "We have not decided and could not decide that there will be no third runway at Heathrow. We have not found that a National Policy Statement supporting this project is necessarily incompatible with the UK's commitment to reducing carbon emissions... or with any policy."

But Will Rundle, head of legal at Friends of the Earth, said: “This ruling is an absolutely ground-breaking result for climate justice. We were fighting a project that would have had dire implications for present and future generations."

It piles pressure on Boris Johnson - who vowed to lie in front of the bulldozers - to axe the Heathrow plan entirely

John Sauven, Executive Director of Greenpeace UK, added: "The third runway is already on its knees over costs, noise, air pollution, habitat loss and lack of access, and now Heathrow Ltd has yet another impossibly high hurdle to clear.

"No amount of spin from Heathrow’s PR machine can obscure the carbon logic of a new runway.

"Their plans would pollute as much as a small country. Boris Johnson should now put Heathrow out of its misery and cancel the third runway once and for all. No ifs, no buts, no lies, no u-turns."

The proceedings concluded at the Court of Appeal in London

The Court of Appeal ruled not against the plans themselves but against the government's procedure in drawing up a National Policy Statement on airport capacity.

That suggests the government must now either rewrite the NPS - drawn up under the rule of bungling Tory Chris Grayling - or drop plans to expand Heathrow entirely.

It comes more than 18 months after Boris Johnson fled to Afghanistan to avoid having to vote on Heathrow Airport's expansion.

An airliner takes off over the rooftops surrounding Heathrow

In 2015 the MP - whose constituency is near the airport - promised he would "lie down with you in front of those bulldozers and stop the building, stop the construction of that third runway”.

But in 2018 he was Foreign Secretary - which meant he'd have to lose his job if he voted against.

After years of dodged questions, in December he repeated his infamous pledge - admitting he would "have to find some way of honouring that promise".

But he added: "Let's wait and see when the bulldozers arrive."

A string of campaign groups and London's mayor challenged the government's National Policy Statement (NPS) - the document that basically gave the green light to Heathrow.

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Heathrow Airport expansion

They brought four separate 'judicial reviews', claiming the proper legal processes weren't followed when the NPS was drawn up and voted on by MPs in 2018.

The campaigners previously lost a High Court fight in May 2019.

But today their cases were to be streamlined together into one mega-ruling at the Court of Appeal.

Together the various campaigns were challenging how the NPS followed (or didn't follow) the rules on habitats, access, noise, costs and climate change.

Issues on air pollution were removed from the case, to be dealt with by a planning inspector at a later date.

The four cases were brought by Friends of the Earth; Plan B; Heathrow Hub Ltd; and Greenpeace together with the Mayor of London and five local councils.