The new runway was approved by the government in 2018, but British Prime Minister Boris Johnson has previously opposed expanding Heathrow, Britain and Europe’s busiest airport.

During last year’s election campaign, Johnson said he would have to find some way of honouring an old promise to lie down in front of bulldozers at Heathrow to halt the expansion plans.

The judge said on Thursday that the government had not sought permission to appeal the ruling in the supreme court, meaning that it will now have to rework the policy if it wants it to go ahead.

Heathrow Airport said, however, that it would be appeal to the Supreme Court, and that recent commitments made by the aviation industry on meeting carbon commitments by 2050 were in with the Paris Agreement.

In his ruling, the judge said that in its current form the government’s policy was unlawful as it failed to take into account climate change commitments made by the government when it signed up to the Paris Agreement in 2015.

“The government when it published the ANPS (Airports National Policy Statement) had not taken into account its own firm policy commitments on climate change under the Paris agreement. That, in our view, is legally fatal to the ANPS in its present form,” said judge Keith Lindblom.

Thursday’s ruling was a victory for environmental campaigners such as Friends of the Earth and Greenpeace, and local authorities who oppose the expansion.

Heathrow Airport, which is owned by Ferrovial, Qatar Investment Authority and China Investment Corp, argues that Britain’s exit from the European Union, makes a new runway critical to ensuring that the UK can continue to increase trade with the rest of the world.

The airport’s two runways are operating at full capacity meaning that it cannot add new flights to drive exports and trade links. In two years, Heathrow be overtaken as the busiest airport in Europe by Paris, whose Charles de Gaulle hub has four runways.

Under the 14 billion pound ($18.2 billion) plan , Heathrow’s new runway would open in 2028. ($1 = 0.7696 pounds) (Reporting by Alistair Smout, writing by Sarah Young; editing by James Davey/Guy Faulconbridge)