London Heathrow airport headed to Britain's highest court Wednesday to challenge a ruling made earlier this year to block a third runway at Europe's busiest hub on environmental grounds.
Hearings at the Supreme Court are expected to conclude on Thursday but a decision may not be announced until early next year.
Heathrow, which is located west of the capital, argues that the Court of Appeal made errors of law in reaching its decision.
Environmental pressure groups Friends of the Earth and Plan B Earth are opposing the challenge.
Britain's government in 2018 gave the green light for Heathrow to expand, with building of the third runway given a 2022 start date.
But campaigners in February won a Court of Appeal case arguing that the government had failed to take into account its own climate change commitments.
Should Heathrow win the case, it will delay construction by at least two years, blaming the move on the legal challenges and coronavirus pandemic.
Britain's largest airport is owned by a consortium led by Spanish construction giant Ferrovial and comprising also sovereign wealth funds from China, Singapore and Qatar.