Plans by Heathrow Airport in England for a third runway have been rejected.

A court decision has blocked the project on environmental grounds.

The UK's Court of Appeal ruled in favour of London Mayor Sadiq Khan, a local council and environmental campaigners - saying that the British government had not considered its commitments to the Paris Climate Agreement.

Britain's Transport Minister Grant Schapps has said the government there will not appeal the decision.

"Airport expansion is core to boosting global connectivity," Mr Schapps tweeted.

"We also take seriously our commitment to the environment. This govt won't appeal today's judgement given our manifesto makes clear any #Heathrow expansion will be industry led."

Airport expansion is core to boosting global connectivity. We also take seriously our commitment to the environment. This Govt won't appeal today's judgement given our manifesto makes clear any #Heathrow expansion will be industry led.

— Rt Hon Grant Shapps MP (@grantshapps) February 27, 2020

Heathrow, however, said it would take the case to the British Supreme Court.

"We will appeal to the Supreme Court on this one issue and are confident we will be successful," the group said a statement.

"In the meantime, we are ready to work with the government to fix the issue that the court has raised.

"Heathrow has taken a lead in getting the UK aviation sector to commit to a plan to get to net zero emissions by 2050, in line with the Paris Accord."

The Court of Appeal judgment was celebrated by campaigners outside the court in London.

Opponents of the runway had argued that former transport minister Chris Grayling ignored factors such as air quality, noise pollution and traffic congestion when he gave the expansion the go ahead in 2018.

File photo of a Heathrow Airport sign in London | Image: Steve Parsons/PA Wire/PA Images

Will Rundle, head of legal at environmental campaign group Friends Of The Earth, was pleased with that prospect, saying climate change should now be "at the heart of all planning decisions".

He added: "It's time for developers and public authorities to be held to account when it comes to the climate impact of their damaging developments."

But despite the ruling, Judge Keith Lindblom said an expansion has not been ruled out.

He said: "Our decision should be properly understood. 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 (NPS) supporting this project is necessarily incompatible with the UK's commitment to reducing carbon emissions and mitigating climate change under the Paris Agreement, or with any other policy the government may adopt or international obligation it may undertake.

"The consequence of our decision is that the government will now have the opportunity to reconsider the NPS in accordance with the clear statutory requirements that parliament has imposed."

The judge added that the court's decision was "not concerned with the merits" of a Heathrow expansion, or of doing nothing to increase the UK's aviation capacity.

"Those matters are the government's responsibility and the government's alone," he said.

The much-delayed Heathrow expansion plans date back to 2003, when a UK Labour government White Paper first recommended a third runway was built.

But the project has been mired by political indecision and local opposition ever since, with alternatives having been sought and cast aside during that time.

Businesses had argued it is crucial to the economy as the airport is already operating at full capacity, leaving the UK at risk of being left behind.

Heathrow bosses had hoped to start work on the runway as soon as next year, and most recent estimates had put completion of the new runway at 2029.