Any attempt to bring forward plans for a second runway at Gatwick would be political suicide, the Government has been warned.

The warning followed claims that Gatwick was one of three airports where Deputy Prime Minister John Prescott has asked British Airports Authority to draw up plans to build a second runway.

There is a legally-binding agreement between West Sussex County Council and British Airports Authority preventing the building of a second runway until at least 2019.

Campaigners anxious to restrict development at the airport say only a Bill in Parliament could wipe out the agreement. They are confident that no Government would risk unpopularity by making such a move.

Brendon Sewill, chairman of the Gatwick Conservation Campaign, said: "It would be a breach of faith and might well not even get past Parliament.

"We are reasonably confident that the legal agreement cannot be overturned and that the Government would not consider it.

"They clearly have two choices. They can put another runway in at Gatwick after 2019 or they they could possibly contemplate annulling that legal agreement before then."

Of the three airports being possibly considered for expansion, Stansted, in Essex, is considered to be the favourite because of its rural location with plenty of land surrounding it.

BAA has plans to improve facilities at Gatwick to handle an expected increase in the number of passengers using the airport.

Airport chiefs insist they have not included a second runway and they have only provided technical information to the Government.

The Government is carrying out a study into airport capacity in the next 30 years. A Department of Transport spokesman said: "The Government has instructed BAA to undertake technical planning facilities studies for Gatwick, Stansted and Southampton, to assist the Government's consultants who are preparing the study.

"BAA will be producing only strictly technical and factual information and will not be offering opinions or making recommendations."