Passengers heading overseas from Gatwick are facing a rise in travel tax in a bid to combat the environmental impact of air travel.

Under plans announced by the Treasury, passenger duty will rise from £5 to £10 for economy flights to Europe and from £20 to £40 for journeys further afield.

This means a family of four would face a price hike of £160 for journeys beyond Europe. The tax, which would hit passengers at all airports, is only payable on the outbound flight.

The announcement came as the Government this week prepared to outline controversial plans to expand Gatwick, a move that would destroy large chunks of the green belt.

A spokeswoman for Gatwick, commenting on the tax proposals, said last night: "At this stage, we are expecting the Government to issue a consultation on the costs of the aviation industry on the environment.

"We will be looking at it in detail and responding in due course. Overall, the aviation industry contributes about £1 billion of passenger duty to the Treasury each year already.

"From a Gatwick perspective, we take the environmental impacts of the airport very seriously. In 2000, we published a sustainable development strategy for Gatwick that sets out the long-term future for growth, which means minimising and mitigating environmental impacts."

A spokesman for the Freedom to Fly coalition, which represents airports and operators, said: "If ministers have to consider a new tax on travellers, then so be it. But they can't have picked a worse time to launch this idea. The industry is just recovering from the effects of September 11, and now we have to brace ourselves for war in the Gulf."

Despite the fears of airports and passenger groups, Dr Caroline Lucas, Green Party Euro-MP for the South-East and the European Parliament's spokeswoman on aviation and the environment, is one person calling for even higher taxes.

She said: "Airlines pay no VAT on new aircraft or the cost of ticketing. Incredibly, aviation fuel is zero-rated too and the industry is shielded from its social and environmental costs.

"The costs of pollution-related ill health, an estimated £1.3 billion a year, are borne by the NHS."

She said if the true cost of flying was passed on to passengers, flying would not be so attractive.

"Studies show if aviation fuel was taxed at the same rate as petrol, 164 million fewer flights would be made annually by 2020."

Gatwick had been excluded from an original consultation process led by Transport Secretary Alistair Darling last summer on airport expansion in the South-East but councils in other areas sought a revue and the High Court ruled the Government should consider Gatwick.

Although it is under no legal requirement to actually choose to develop Gatwick, which currently has one runway, residents in the West Sussex area are furious that the airport is back on the expansion map.