Airlines in Europe and Africa vowed yesterday to cancel flights rather than comply with American demands to carry armed air marshals on some US-bound planes to guard against more September 11-style attacks.

The decisions by South African Airways and Thomas Cook Airlines, the charter flight arm of Europe's second biggest travel firm, deepened controversy over a move Washington sees as essential to outwitting al Qaeda and other extremist groups.

The British government insisted it would deploy marshals where appropriate.

Another jet was delayed in London overnight as protracted security checks could not be completed in time for takeoff.

British Airways' flight BA183 from London's Heathrow to New York's John F. Kennedy airport, with 262 passengers, was now due to leave nearly a day late at 1530 GMT, BA said.

The Christmas and New Year global aviation scare has already grounded British flights to Saudi Arabia and Washington.

British Transport Secretary Alistair Darling said tighter security would be needed indefinitely and more delays would follow.

Media speculation has suggested intelligence services have specific information about al Qaeda plans to down planes.

"This state of alert is likely to last for some considerable time, " Mr Darling told parliament. "We will continue to be vigilant, we will continue to do what is necessary."

British pilots - unhappy with air marshals but starting to see them as inevitable - were due to meet Mr Darling later yesterday to press for an industry-wide agreement on their deployment.

"The fact that you have got people behind you in a pressurised cabin with guns and bullets is not a happy thought," said a spokesman for the British Airline Pilots' Association (BALPA), which groups most of Britain's 9,200 airline pilots.

"But if the government persists, we want certain conditions laid down."

Mr Darling insisted sky marshals would be used on flights from Britain because of a heightened terror threat.

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