Conservationists fear the Government is about to "tear up" an agreement that prohibits a new runway being built at Gatwick airport.

A covenant signed in August 1979 prevents a new runway before August 2019.

The Gatwick Area Conservation Campaign (GACC) group is worried that the Government may have found "a way round" the agreement or will introduce legislation to change it.

Proposals about new airport and runway expansion in the South East are due to be published by the Government in consultation papers next month.

"We would like to think the Gatwick agreement is watertight," said GACC chairman Brendon Sewill.

"However, if legislation is brought in to overturn the covenant, we are hoping that the House of Lords will block it.

"People living near Heathrow and Stansted airports are also very keen not to have additional runways. The areas just cannot sustain any expansion.

"Ideally, we hope the Government goes for the option of a new, coastal airport for south-east England."

It is thought that the building of a new airport close to the Thames estuary at Cliffe in Kent is one option being considered by the Government.

But airlines would consider such a site to be too far away from central London.

Last Tuesday, transport minister John Spellar said air fares could rise by as much as £100 for each return journey if airport infrastructure was not expanded.

British Airways last week proposed the building of a new, short northern runway at Heathrow - a move opposed by Heathrow anti-noise groups.

The newly-privatised National Air Traffic Services believes expanding existing airports is a better move than creating a new airport.

Final decisions are expected in an aviation White Paper - the first for many years - due out in a few months.