The government has been urged to be more specific about when and where new runways should be built.

Alastair Darling is reluctant to say which airports in the South East should be developed first. He is also unwilling to publish a timetable for opening the three runways needed in the South East for the projected tripling of demand for air travel.

Businesses, airlines and union leaders have written to the transport secretary to protest.

"It is essential that ministers provide the greatest possible clarity...and also make clear which runway the government believes should be developed first," says a letter signed by Digby Jones of the CBI, Brendan Barber of the TUC, Mike Clasper of BAA and Richard Branson of Virgin.