The Government today suffered a shock defeat in a legal challenge over its ruling out of a second runway at Gatwick Airport.

The High Court judgment relates to the Government's handling of consultations relating to airport expansion in the South East.

A judge agreed with complaints from Kent and Essex that the consultation process being used by Transport Secretary Alistair Darling was flawed because it left out the possibility of expansion at Gatwick in the near future.

Mr Justice Maurice Kay, sitting in London, said: "The applicants have succeeded."

He was allowing a legal challenge by Essex, Kent and Medway councils opposing the expansion of Stansted Airport in Essex, or the option of a major new airport at Cliffe in Kent.

After giving his ruling, the judge was going on to decide whether to quash the decision excluding Gatwick - or to quash the consultation exercise as a whole.

Lord Hanningfield, leader of Essex County Council, said after the ruling: "We feel that it is vitally important, not just for the South East, but the whole of the UK, that all possible options for meeting the growing demand of air services in the UK are considered, including Gatwick.

"We want to be clear that this action was not motivated by a desire to push development on to that airport.

"However, we believe that 95% of demand in the South East up to 2015 could be met through making maximum use of all available capacity."

A 40-year legal agreement between West Sussex County Council and airport operator BAA, signed in 1979, prevents any second runway before 2019.

A Transport Department spokesman said: "The decision in the spring not to propose another runway at Gatwick was driven by our conclusion that it would be wrong to seek to overturn the legally binding agreement entered into by BAA in August 1979."

The judge gave Government lawyers permission to appeal to the Court of Appeal, saying the case was of "considerable importance".

He ordered the Transport Secretary to pay legal costs to his opponents, unofficially estimated at not less than £100,000.