IN Honduras, they insist on cash: a wad of crumpled, sweaty lempira. In Australia, you can buy a dollars 20 departure- tax stamp in advance from post offices. But Britain's new Air Passenger Duty, which comes into effect this autumn, is causing confusion among airlines, travel agents, government and travellers.

From 1 November, people taking a flight from Britain to countries within the European Union will pay pounds 5 tax; those flying beyond it, pounds 10. The money is not for improving airport facilities: it is purely a revenue-raising device.

Most air tickets are bought through travel agents, who are receiving conflicting advice from different carriers. Some airlines insist that agents add the tax now to tickets for departures from 1 November onwards, others that passengers will have to pay at the airport. A Treasury spokesman I talked to compared the new tax to Budget increases in alcohol and tobacco duty, ie buy now to dodge the tax. But Customs and Excise (the department charged with collecting it) insists that, regardless of when you buy the ticket, all air travel from Britain after 1 November will be subject to tax.

The amount you pay is also open to question. Supposing you fly from Edinburgh on British Airways to Heathrow, connect there for the British Midland flight to Frankfurt, which in turn feeds into the Royal Brunei service to Singapore - a not-unreasonable route. Depending on how your agent calculates it, you could pay pounds 5, pounds 10 or pounds 15 in tax.