Opponents of the proposed third runway at Heathrow have beaten the Government at the High Court in London.
Lord Justice Carnwath agreed with Councils, residents and green lobbyists that the public consultations that lead to the approval of the new runway were flawed.
The decision does not mean the runway will not be built, but ministers will have to carry out fresh consultations with affected groups.
Lord Carnwath said called for a review of "all the relevant policy issues, including the impact of climate change policy.
The ruling is a major blow to the Labour government with only seven weeks until the general election.
However, the Department of Transport said it would "robustly defend" the third runway plan.
The Conservatives have, as expected, criticised Labour's transport policy, saying they were in complete accordance with the decision.
However, it is known in Whitehall circles that many Tory backbenchers are not comfortable with David Cameron's vehement opposition to the third runway.
A source close to the Tory Party told ABTN: "There is concern that we've put all our eggs in one basket, when we should have sat on the fence. There are a number of party members who believe the third runway would be beneficial to the UK economy, but are having to toe the party line before the election."
In his ruling, Lord Justice Carnwath said: "Whether there should be a third runway at Heathrow Airport is a question of national importance and acute political controversy.
"It is a matter on which the main parties are currently divided and which may well become a significant debating point at the forthcoming general election."
The hearing was adjourned until after Easter to give both sides time to consider what formal orders the court should make.