Terror in the sky: the net tightens

A week of terrorist alerts that has caused disruption on a scale not seen since 11 September 2001 culminated in dramatic scenes at Heathrow airport yesterday, when a British Airways flight to Washington DC was barred from taking off, for the second successive day, because of a specific terrorist threat.

BA flights to and from the Saudi Arabian capital, Riyadh, were also cancelled after warnings from British intelligence services. BA 263, which was to take off from Heathrow at 1.35pm today, and BA 262, due to leave Riyadh at 2am on Sunday, were cut from the schedule.

There was no sign yesterday that the US authorities were ready to relax the code orange terrorist alert - the second highest level - imposed 10 days ago to safeguard America during the holiday period.

Not since September 2001 have the strings of America's anti-terrorist net been so tightly drawn. Even though none of the feared Christmas attacks on America materialised, the effect is being felt around the world.

Some of the most disruptive consequences of the alert have been felt by BA's flight 223, which leaves Heathrow at 3.05pm daily for Dulles airport in Washington. The flight was again held at the airport yesterday. The last time the Boeing 747 was allowed to fly - on New Year's Eve - it received an escort of two US F-16 fighters. It was directed to a corner of the airfield far from the terminal and, for the next three and a half hours, passengers were interviewed by security officials before they were allowed to disembark.

Although two other BA flights from London to Washington took off as scheduled yesterday, flight 223 was grounded because it was the subject of specific information, security sources said. US officials insist the measure is spurred by credible intelligence.

Passengers were still being checked in for yesterday's flight just minutes before BA announced the cancellation. The airline said as many passengers as possible were put on a later flight, at 6.35pm, and some of the others would be travelling today. A BA spokeswoman was unable to say whether today's flight 223 would be affected.

US intelligence believes that al-Qa'ida is plotting an attack more devastating than those of 2001. Against that background, governments and airlines have little choice but to co-operate. During the past month, intelligence agencies in the US, Britain, Europe and the Arab world have received repeated warnings of an attack at about this time. Telephone intercepts by Britain's GCHQ listening post at Cheltenham and the National Security Agency in the US are said to have indicated that an aircraft would be used in the attack - with Los Angeles and Washington airports particular targets. There have been warnings about attacks on British targets, leading to the closure of the embassy in Lima, Peru, and a strong warning to British citizens not to travel to Saudi Arabia.

On Monday, the US in effect demanded all carriers should be ready at any time to place armed marshals on planes. The order came hours after Britain announced plans to place marshals on flights to America.

In the US, there has been no sense of panic. But the new security steps have not gone unnoticed. Snipers watched over revellers in Times Square on New Year's Eve and fighter planes have been patrolling the skies above cities including Las Vegas. This week, the Coast Guard temporarily halted the transfer of oil to tankers at the Alaskan port of Valdez because of fears the terminal might be a target.

The authorities are now focusing on BA's daily flight 223. Paul Beaver, a defence analyst, said: "The intelligence is very, very precise which is why this one flight has been cancelled. We have got intelligence, I am told, that there was a plan to take the aircraft and destroy it over Washington or fly it into something. Washington is the definite target."

Although the City seemed largely unconcerned yesterday about the impact of the terror alert on airlines - BA shares fell just 3p to 229.5p - the airline industry cannot afford to suffer a repeat of the downturn which followed 11 September.

Flight disruption began on Christmas Eve when, acting on information from the US, the French government ordered Air France to suspend flights to Los Angeles. Six jets were halted in two days. On Wednesday and Thursday, Aeromexico flights from Mexico City to Los Angeles were cancelled. On Thursday, an Air France flight to New York made an unscheduled landing in Canada for its luggage to be checked.

The Wall Street Journal reported yesterday that the cancellation of the Air France flights on Christmas Eve was the result of US officials wrongly identifying passengers as possible terrorist suspects. French officials saidone passenger whose name matched that on an "alert" list turned out to be a child; another turned out to be Welsh insurance agent; while a third was an elderly Chinese woman.

In an embarrassing development for the US authorities, Charles Brady, the head of the transport security administration at Dulles airport, was arrested for drink driving on New Year's Eve, shortly after passengers on BA 223 had been released from questioning. He was meant to have stayed at his post at Dulles until 2am. Police said he was stopped at 1am.

A man carrying two knives and talking about the end of the world on a Luton-bound flight was arrested by Spanish police yesterday. The Chilean was detained after an easyJet plane taxied for take-off at Barajas airport, Madrid, on Thursday. Police found two penknives on the man that had not shown up on a metal detector.