Families will save up to £200 on a long-distance flight if they go via a European airport rather than flying direct because of a loophole in the Government’s new green tax on aviation.

Passengers can avoid paying tax on the whole journey by changing planes on the Continent, where the tax does not apply. Under the existing tax, which is being abolished, they are charged the same rate regardless of the route.

Ministers claim that the tax will reduce pollution from aircraft but overall emissions will be higher for the thousands of people who save money by catching two flights instead of one and flying hundreds of miles farther. Many will fly east to Paris or Amsterdam before catching connecting flights west to the United States, meaning they will pass back over Britain.

Alistair Darling, the Chancellor, announced last October that the existing direct tax on air passengers would be replaced by a tax on aircraft “to ensure the industry makes a greater contribution towards its environmental costs”. The announcement was rushed out after the Conservatives had proposed the idea at their party conference a few days earlier.

At present, economy-class passengers pay £10 in air passenger duty for short-haul and £40 for long-haul flights. Business and first-class passengers pay £20 for short haul and £80 for long haul.

The new aviation duty, coming into force in November next year, will be paid by airlines. They will pay a fixed sum for each flight, depending on the distance and the weight of the aircraft. The duty will not vary according to the number of passengers carried and will therefore encourage airlines to fill as many seats as possible to spread the cost.

But the duty will only be payable on flights departing from UK airports. Passengers who fly long-haul via a European airport will only have to pay their share of the tax on the initial short-haul flight.

The Government is also raising the overall amount collected in aviation tax from £2.1 billion in this financial year to about £3.6 billion in 2011-12.

The British Air Transport Association (BATA), which represents British Airways, Virgin Atlantic, bmi and 13 other British airlines, said that passengers would pay 75 per cent less tax by flying via a European airport. On routes of more than 3,000 miles, the tax on direct flights will be up to £50 more per person – £200 for a family of four.

Roger Wiltshire, the BATA secretary-general, said: “The new duty will subsidise foreign airlines and airports and damage the environment because people will take off twice and fly longer. It will also damage the economy by undermining our own industry.”

A spokesman for the Treasury said the finer details of the new tax had yet to be decided but it believed few people would be willing to change planes for the sake of lower fare. But Air France-KLM said more than 600,000 people a year already flew from London to Paris or Amsterdam to catch onward long-haul flights.

A spokesman said even a small difference in the fare was enough to attract people to fly through a European hub, where connection times are typically 45 minutes, half the time that it takes to change planes at Heathrow.

Regional airports in Britain are also concerned that the new tax will result in airlines reducing services to Heathrow.

Graeme Mason, head of planning at Newcastle airport, said: “Whether intended or not, the Government is discriminating against UK airlines and airports in favour of overseas airlines and airports.”

Times recommends

• Travel advice: what to do if your flight is disrupted
• Top 10 unmissable events in 2010
• Seven spa breaks for January