The plans to build a third runway at Heathrow look to be back on after the UK Supreme Court overturned a Court of Appeal decision against the expansion back in February.

The court has ruled that the government acted lawfully in in approving the £14bn project so in theory Heathrow can now proceed with its expansion plans, though the massive drop-off in aviation travel demand due to the covid-19 pandemic could delay those plans further.

A panel of five judges decided that former transport secretary Chris Grayling had acted lawfully when he approved the third runway project by relying on domestic legislation, rather than the Paris climate agreement. The justices agreed with Heathrow’s lawyers who argued that the then transport secretary did not need to consider the Paris agreement when drafting Heathrow policy as this “could not constitute domestic policy as it was a global aim”.

In a judgement that could have implications for other major infrastructure projects going forward, Heathrow’s lawyer, Lord Anderson QC said: “The Paris agreement sets a global long-term temperature goal, not national targets and a global aim is incapable of being government policy for the purposes of assessing carbon effects of an individual development scheme.”

A Heathrow spokesperson said: “This is the right result for the country, which will allow global Britain to become a reality. 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. Demand for aviation will recover from Covid, 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 has already committed to net zero and this ruling recognises the robust planning process that will require us to prove expansion is compliant with the UK’s climate change obligations, including the Paris Climate Agreement, before construction can begin.”

The court’s decision was welcomed by construction sector leaders. Civil Engineering Contractors’ Association director of external affairs Marie-Claude Hemming said: “To secure the long-term interests of the UK, we must close the aviation capacity gap. Heathrow is key to Britain’s status as a global trading nation, and its expansion will deliver many thousands of jobs and billions of pounds to the UK economy. The £14bn expansion will be privately funded, which means it will be built at no cost to the taxpayer and will address the fact that Heathrow has been operating at full capacity for many years.”

Hannah Vickers, chief executive of the Association for Consultancy and Engineering, said: “The carbon challenges for the aviation sector are well understood, but expansion at Heathrow is not necessarily incompatible with a carbon-free future. These kinds of decision need to be made as part of a comprehensive net zero strategy for the country, not taken in isolation.

“Today’s court ruling does mean that the major project is one step closer however, and the £14bn plan is proof that private investment can play a key role in our economic recovery. The core take-away is that we should update our national policy statements to ensure they are compatible with net zero ambitions. This would ensure the right future infrastructure projects can proceed with confidence while avoiding unnecessary uncertainty and legal delays.”