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Plans to build a third runway at the UK airport Heathrow may not go ahead after a court ruled it illegal.

The Court of Appeal said the expansion was unlawful because it did not take the UK's climate commitments into account.

The judges said that in future, a third runway could go ahead, as long as it fits with the UK's climate policy.

The decision was a victory for environmental groups, councils and the Mayor of London that had brought the challenge to court.

Heathrow Airport said it would oppose the decision, but the government is not going to appeal.

Supporters of the runway say it would boost the whole UK economy because businesses would be able to deliver more goods.

The court of appeal said the government had failed to follow the Paris Climate Agreement to limit global warming.

The judges said it was "legally fatal" to the government's Heathrow expansion policy that it did not take those climate commitments into account.

Heathrow will now have to go directly to the UK Supreme Court to appeal the decision.

The Â鶹ԼÅÄ's environment analyst Roger Harrabin said that this could mean that future building projects could face legal challenges if they fail to meet the aims of the Climate Change Act, which promises virtually zero emissions by 2050.

He also says: "The prime minister's decision not to appeal against the ruling may also call into question aviation expansion in other airports, as there is currently no viable technical fix to make planes zero-carbon."