Heathrow’s third runway will not be built until at least 2030, lawyers for the airport told Britain’s highest court this week.

The west London airport wants to expand its five terminal base with a new runway, which could increase flights by up to 700 a day.

The third runway was originally expected to open in 2026 – but the airport is now battling to save its expansion plans, after the Court of Appeal ruled them unlawful on environmental grounds.

Britain’s second highest court said in February that Heathrow should have taken the Paris Agreement – a 2016 international commitment to limit global temperature rises to 1.5C – into account.

This week, the airport went head to head with Friends of the Earth and environmental litigation charity Plan B in the Supreme Court, arguing that its expansion plans are compatible with climate change policy.

Lord Anderson, the lawyer for Heathrow, said Britain already has tough domestic laws to tackle global warming.

“These are achievements for which the overused term world-beating is, we submit, justified,” he told the court on Wednesday (October 7).

Mr Anderson said the Government was not obliged to consider the Paris Agreement when signing off airport expansion, and there had been ample opportunity for scrutiny.

“This is not some capricious decision by a minister but a long term policy debated in parliament,” he argued.

MPs voted 415-119 for a third runway at Heathrow in June 2018. Prime Minister Boris Johnson – then Foreign Secretary – was in Afghanistan at the time.

Mr Johnson had refused to quit the Government to vote against the plans, despite previously promising to lie in front of bulldozers to stop airport expansion in his Hillingdon constituency.

But Heathrow has now admitted that even in a best case scenario the third runway will not open until 2030.

As well as the ongoing legal battle, Heathrow, like other airports, has been hammered by Covid-19 – with with passengers down 90 per cent at the peak of the virus.

“Even if everything went smoothly from this point on, [the third runway] could not open until 2030 at the earliest,” Mr Anderson told the court.

But climate change groups argue that the expansion plans should not be allowed at all, and the Court of Appeal was right to rule them unlawful.

David Wolfe, lawyer for Friends of the Earth, said it was “absolutely obvious” that ignoring the Paris Agreement would be “irrational”.

“There was emerging thinking within Government that could have altered that conclusion, and might have made a difference to the Airports National Policy Statement designation decision [which backed the third runway].”

But Mr Anderson said ministers were not obliged to take into account new ideas “the moment civil servants start thinking” as this would be “a recipe for chaotic government”.

The two day virtual hearing has now concluded, and a ruling from the court is expected in January.