Prime Minister Tony Blair stepped in to the row over the future of Gatwick by voicing regret at a ruling which has re-ignited the prospect of expansion.

Mr Blair said he would understand if people living near the airport felt aggrieved at the U-turn, which could lead to a second runway.

He spoke after the Government was forced to bow to a High Court demand that Gatwick must be included in national aviation expansion plans.

During his weekly question session in the Commons, MPs demanded to know why Gatwick had been excluded last July.

Mr Blair said the Government had wanted to stick by a 1979 agreement that there should be no growth at the airport before 2019.

He said: "The reason why we excluded Gatwick was because we had given an undertaking we would.

"However, the court has said it must go back in and that is what will happen."

On Tuesday, five judges unanimously ruled Gatwick should have been part of the consultation after a legal challenge from councils in Essex and Kent.

Yesterday Transport Secretary Alistair Darling said: "I believe it would be wrong to extend the uncertainty that would inevitably result from a lengthy appeal process and so I have therefore decided to accept the judgement."

A consultation exercise on building a second runway at Gatwick will now be launched.

The move has delayed the conclusion of the Government's Aviation White Paper, which will outline a firm proposal for boosting air capacity, until next May.

The councils and local residents rejoiced at the news while in Sussex feelings are mixed.

Businesses generally back the idea of a second runway, while residents are concerned about increased pollution and noise.

Brendon Sewill, of the Gatwick Area Conservation Campaign, said:

"The decision will cause a huge amount of blight and anxiety, not only around Gatwick but around all the places proposed for airports because it will be delayed."

Sussex Enterprise chief executive Mark Froud said 87 per cent of Sussex businesses surveyed said a second runway would be good for their business and the local economy.

But Tex Pemberton, Cabinet member for West Sussex County Council's strategic environmental services, said he deplored the decision, adding: "Creating a second runway at Gatwick would cause appalling damage to the countryside and environment."