Britain's Supreme Court on Wednesday ruled that Heathrow, one of the world's busiest airports, can build a third runway, overturning a legal decision to block the plan on environmental grounds as the aviation industry looks to recover from the coronavirus pandemic.

The nation's highest court struck down a Court of Appeal ruling in February that the UK government had failed to take into account climate change commitments when in 2018 it approved the new runway at the London airport.

Heathrow successfully argued that the Court of Appeal had made errors of law.

Following the latest ruling, Friends of the Earth insisted the ruling was not a green light, saying the judgement still required Heathrow to address climate concerns.

Greenpeace urged Prime Minister Boris Johnson to scrap the project, in the light of his government's targets on cutting carbon emissions.

Five years ago Johnson infamously vowed to lie down in front of the bulldozers to stop the runway being built.

It was his predecessor Theresa May who in 2018 approved a third runway, while Johnson has ignored his bulldozer pledge as he trumpets big infrastructure projects to help drive Britain's post-Brexit economy.

The Supreme Court said that the previous Conservative government had "no obligation" to consider the Paris climate agreement when it gave the nod to the extra runway.

While the UK government said building work could begin in 2022, Heathrow warned that it would delay construction by at least two years owing to the legal challenges and the coronavirus upheaval.

Heathrow airport hailed Wednesday's ruling, which it said would also allow Britain to compete with continental rivals following Brexit.

"Only by expanding the UK's hub airport can we connect all of Britain to all of the growing markets of the world, helping to create hundreds of thousands of jobs in every nation and region of our country," it said in a statement.

"Demand for aviation will recover from Covid-19, and the additional capacity at an expanded Heathrow will allow Britain as a sovereign nation to compete for trade and win against our rivals in France and Germany."

Heathrow said its Terminal 4 would remain closed until the end of next year because of the slump in passenger numbers
Heathrow said its Terminal 4 would remain closed until the end of next year because of the slump in passenger numbers AFP / Adrian DENNIS

The airport added that it had "already committed" to net zero carbon emissions and that the latest ruling "recognises the robust planning process that will require... expansion is compliant with the UK's climate change obligations, including the Paris Climate Agreement."

"This judgement is no 'green light' for expansion." said lawyer Will Rundle on behalf of Friends of the Earth.

"It makes clear that full climate considerations remain to be addressed and resolved at the planning stage.

"Heathrow expansion remains very far from certain and we now look forward to stopping the third runway in the planning arena," he added.

Greenpeace UK meanwhile urged the government to scrap the project.

"Now the ball is in the government's court, it's hard to imagine Boris Johnson wanting to resurrect a project that makes no business or environmental sense," said Greenpeace executive director John Sauven.

"With a UK-hosted climate summit just a year away, the government should draw a line under this sorry saga."

The ruling comes as the Covid-19 pandemic devastates demand for international air travel.

Heathrow last week said its Terminal 4 would remain closed until the end of next year because of the slump in passenger numbers.

Heathrow is owned by a consortium led by Spanish construction giant Ferrovial.

It includes also sovereign wealth funds from China, Singapore and Qatar as well as North American shareholders.

Despite remaining one of the world's largest airports, Heathrow was this year overtaken by Paris Charles de Gaulle as Europe's top hub in terms of passenger numbers -- blaming its relegation on delayed coronavirus testing and travel restrictions.