ONE MONTH from today, the new air passenger duty comes into effect, adding pounds 5 or pounds 10 to the cost of flights from the UK. The tax means that a substantial proportion of fares to the US is made up of levies. Virgin Atlantic (0293 747747), for example, charges pounds 25 on its basic London-New York fare of pounds 278 from 1 November. United Vacations (081-313 0999) includes all taxes in its US city breaks, such as three nights in New York for pounds 355 or a week in Seattle for for pounds 499, including flights from Heathrow or Glasgow.