London Heathrow, Europe’s busiest airport, overcame an attempt by environmental groups to block construction of a third runway that it says is needed to boost flights and compete with rival hubs trying to steal its traffic.

Construction can go ahead after judges on Wednesday threw out lawsuits from Friends of the Earth, London Mayor Sadiq Khan and other groups seeking to challenge the U.K. Government’s approval of the plan.

Opponents alleged the proposal violated the U.K.’s climate change policy and didn’t take account of the Paris climate accord. But that agreement isn’t part of British law, even though the country has ratified it—and this posed an “overarching difficulty” to the lawsuit, the three judges said.

Though it can still be appealed, the decision reduces the risks involved with a lawsuit that could’ve become a major stumbling block for the third runway plan. If the government had lost the case, it would’ve had to start the process again, potentially causing delays and uncertainty.

‘Strong Views’

“We understand that these claims involve underlying issues upon which the parties—and indeed many members of the public—hold strong and sincere views,” the judges said in the unanimous ruling.

They added that the hearing had concerned only the legality and “not the merits” of a government policy statement that approved the expansion.

Heathrow is “delighted,” a spokesman said. “The debate on Heathrow expansion has been had and won, not only in Parliament, but in the courts also.” It’s preparing to unveil a “masterplan” for the project in June, it confirmed in an earnings statement Wednesday, including a detailed blueprint for the new landing strip and associated physical infrastructure such as passenger terminals.

Transport secretary Chris Grayling said the court’s decision is “welcome” and Heathrow expansion “will provide a massive economic boost.”

Virgin Atlantic, which operates most of its flights from Heathrow, said it will target a greater percentage of takeoff and landing slots. “Without the third runway, Virgin Atlantic cannot realize its ambition to become the U.K.’s second flag carrier,” the airline said.

Appeals

Plan B, one of the groups that challenged the expansion, expects to appeal the ruling. Friends of the Earth and Heathrow Hub, two other opponents, will consider doing so, they said in statements. London’s Deputy Mayor Shirley Rodrigues said Khan “stood up for Londoners” by bringing the case, and hasn’t decided his next steps yet.

After decades of delays tied to concerns about extra aircraft noise, increased pollution, the demolition of homes and the impact on roads, construction of the runway could begin as soon as 2021, officials said last year. The new landing strip is expected to open in 2026, lifting annual capacity to 135 million travelers from 2018’s 80.1 million.

The runway was approved by Parliament in June as part of a national policy statement, helping to minimize further procedural logjams, with planning authorities confined to considering elements of the proposal rather than whether it should be built at all.

The airport operator has spent years trying to win permission to build the new runway. In 2018, it was only able to boost flight numbers 0.2 percent because of a shortage of slots.