The US authorities were due to decide late last night whether to reopen North American air space after the unprecedented suspension of civil flights in the wake of Tuesday's atrocities.
If airlines are allowed to resume flights today, the US Government will insist on ultra-tight security, and it was unclear whether full schedules are feasible. Where airlines sought to operate to existing timetables, it could take several days for services to get back to normal because planes diverted away from the USA are now in the wrong place.
Passengers on flights from and within Britain yesterday were the subject of extremely tight security, while armed police mounted extra patrols at airports and special forces were placed on high alert.
Experts predicted that the disasters in America would have a "catastrophic" long-term impact on airlines as fares rose to pay for enhanced security and some carriers went out of business.
Travellers leaving British airports yesterday were the subject of body searches, and the Government ordered that hand luggage should be searched a second time before passengers boarded planes. Some airlines banned all bags from cabins.
Flights were delayed by up to one and a half hours by the extra security, but disruption was kept to a minimum because airports were relatively empty and take-off slots were more flexible in the absence of transatlantic services. Small private flights were banned, giving more air space to planes still operating. At one stage, however, the low-cost carrier easyJet cancelled flights because it predicted that tight security would lead to congestion.
No flights were allowed over the centre of London, and government officials confirmed that aircraft could be shot down for breaching the order.
City of London airport, where flights come within a few thousand feet of the Canary Wharf tower, was closed, and it was not known last night when it would reopen.
British holidaymakers headed for North America will be offered compensation, tour operators said. Anyone due to take to take a package holiday in New York, Boston or Washington within the next seven days will be offered alternative destinations or full refunds. The offer applied to the rest of the USA and Canada, but only to passengers due to travel within the next 48 hours.
The cancellation of transatlantic flights meant that hundreds of Americans were forced to wait at airports, although airlines were able to arrange accommodation for some of them. Hotels were urged to offer free rooms to those unable to pay.
Apart from services to North America, British Airways also suspended its flights to Pakistan and Israel, although the Israeli airline El Al continued to operate.
The British Incoming Tour Operators Association expressed fears that the number of Americans travelling abroad would be drastically cut. Some 4 million US visitors come to Britain every year – the biggest single group.
Chris Yates, aviation security editor at the journal Jane's Transport, said there would have to be a radical rethink of security measures at American airports. "Lax" scrutiny of passengers and their baggage clearly allowed the terrorists on board the aircraft on Tuesday with little difficulty, he said.
"Eighteen months ago I flew from Phoenix to Manchester via Cincinnati and New York and there was no evidence of security at any of the US airports," he said.
Mr Yates was body-searched yesterday before boarding a flight from Manchester to London, and asked to switch on his computer and mobile phone to ensure they were not bombs.
He argued that security at British airports was the best in the world and forecast that the atrocities in America would have little long-term impact in this country.
One American yesterday e-mailed Radio 5 Live reporting that he had recently got on a flight from the USA to Britain, and a knife he was carrying was only discovered when he tried to board a plane at Luton bound for Scotland.
The International Air Transport Association called on its 275 member airlines around the world to tighten security procedures. William Gaillard, an Iata spokesman, said the attacks showed the need for more modern technology – including iris and palm scanners – to thwart potential terrorists trying to board aircraft. "We need to look at all procedures all over the world and see whether there are any loopholes," he told Reuters.
Iata put the iris-scanning system, developed by US-based companies, on display at its annual general meeting in Madrid in May.
"By scanning the iris and the palm of the hand, you can transmit information electronically," Mr Gaillard said. "It is safer than using a passport and photo for identification because it is unique."Reuse content