A minister has hinted that the Government may be prepared to sanction the building of new airport runways in the South-East.

One of the options under consideration is at least one new runway at Gatwick.

Transport minister John Spellar said air fares could rise by £100 a journey unless new runways are built to relieve congestion.

His words were being seen as a clear signal that ministers are prepared to sanction the building of new runways - a move that would alarm local residents and environmentalists.

Mr Spellar said failure to meet the demand for additional air travel - expected to double by 2020 - could cost the national economy up to £20 billion.

He was to give his speech yesterday to a conference in London organised by the Centre for Transport Policy.

But he chose not to attend out of respect for the Queen Mother and the speech was delivered on his behalf by a Transport Department official.

In the text of his speech, Mr Spellar said that officials had worked out the possible economic benefits of meeting the extra demand for air travel in the South East.

He wrote: "Constraining the South East could drive several tens of millions of passengers away from UK airports altogether."