Washington seeks power to ban air travellers - even if they are only flying OVER the U.S.

The US government is demanding the right to ban British air passengers from flying over America en route to other countries – even when the flights will not land in the United States.

Under anti-terrorism measures due to come into force within two years, the US authorities insist they need to do background checks on all UK air passengers travelling to Canada, the Caribbean, Mexico and South America.

Direct flights to popular holiday destinations such as the Bahamas, Barbados, Toronto and Mexico City would all be covered by stringent US security checks examining people's passport details, travel plans and even how they paid for their ticket.

US security officials insist the checks must be completed 72 hours before departure or the flight will be banned from US airspace.

Anyone identified as having "suspicious indicators associated with travel behaviour" by US security would be prevented from boarding their flight.

Almost every flight leaving Britain and Europe for North and South America will be affected.

For safety reasons, transatlantic flights usually take the shortest route across the Atlantic and then fly over or close to the US coast so they can divert to an airfield quickly in an emergency.

The far-reaching new demands emerged last month during a private meeting between US Homeland Security Secretary Michael Chertoff and Jacqui Smith, the Home Secretary, but have not been revealed until now.

Mr Chertoff confirmed British passengers would be checked against US anti-terror and so-called "no-fly" lists.

Miss Smith said: "We agree that it is possible to maintain that ability for people to travel whilst at the same time building on the close relationship we have in sharing information, in ensuring that we're working together to develop the strongest security around travel between our countries."

Civil liberties campaigners fear the Secure Flight programme could be used to gather information about anyone flying, not just those with links to terrorism.

The Home Office insisted: "No decisions have been made."