Lawyers, scientists and legal academics have signed a letter to the Supreme Court, urging it to consider the ‘grave implications’ of its ruling on Heathrow’s third runway.

Almost 150 experts, including the government's former chief scientific adviser Sir David King, claim the judgment undermines the UK’s status as a ‘champion of the Paris Agreement’ in a letter to Supreme Court president Lord Reed. In December, the Supreme Court unanimously overturned a Court of Appeal judgment that a third runway at Heathrow airport was illegal.

‘We urge you to consider the grave implications of this judgment,’ the letter states. ‘The highest court in the United Kingdom has set a precedent that major national projects can proceed, even where they are inconsistent with maintaining the temperature limit on which our collective survival depends.

‘Indeed, the precedent goes further still. It says that the government is not bound even to consider the goals of an agreement that is near universally agreed. Not only does that undermine the UK’s status as a “champion of the Paris Agreement”, just ahead of the critical climate talks in Glasgow later this year. It also substantially reduces humanity’s prospects of maintaining that limit and hence, averting disaster.’

An environmental lawyer involved in the Heathrow case is to be prosecuted for contempt of court after leaking the court’s decision a day before judgment was due to be delivered. Tim Crosland, a barrister and director of eco-charity Plan B Earth, described his actions as ‘civil disobedience’.

The signatories of today’s letter said they understand why Crosland ‘felt it necessary to raise the alarm about the goals of the Paris Agreement being ignored by British courts’.

‘With all that is at stake, in the UK and beyond, we urge the court to take appropriate steps to mitigate the profound harm its judgment has caused and to consider the actions of Tim Crosland in this light,’ it said.

Signatories include climate activist solicitor Melanie Strickland and Paul Powlesland, a barrister at Garden Court Chambers and founder of Lawyers for Nature. Dr Andrew Jackson, an environmental and planning solicitor who previously worked for Slaughter and May, and Stephen Clarke, a retired solicitor advising Bristol Airport Action Network, also signed the letter.