Conservationists fear pressure from the aviation industry could shoot down a pledge not to build a second runway at Gatwick before 2019.

The Freedom To Fly campaign, a coalition of UK air users, is calling for long-term growth in UK aviation in the next 30 years to cope with rising demand.

But today Brendon Sewill, of Gatwick Area Conservation Campaign, said: "We believe this group was set up to influence the Government's decision in favour of new runways in the South East.

"It would be surprising if Government consultation papers did not include Gatwick as an option."

The South East and East of England Regional Air Services study was set up by the Government two years ago to look at airport capacity. Options, to be announced at the end of March, could include a new airport.

A final decision about the number and location of runways will be made at the end of the year.

Mr Sewill said forecasts showed air travel would treble by 2039 and would need the equivalent of six new Heathrows or 12 new airports the size of Gatwick.

He said: "We are putting our trust in the legal agreement and hope the Government will resist pressure from Freedom To Fly."

Mr Sewill said the legal agreement could be overturned by Parliament but he did not think the House of Lords would agree because it would be widely seen as a breach of faith.

Even if the threat of a second runway at Gatwick was removed, the group is concerned expansion would increase noise, pollution and loss of countryside.

Mr Sewill said: "The forecast growth is largely due to unrealistic low prices because aviation pays no fuel tax, no VAT and no tax on the damage it causes to the environment. Health and education are starved of funds while air travel goes almost tax free."