THOUSANDS of passengers faced delays after an air traffic control computer glitch brought chaos to UK airports yesterday.

The fault on the 30-year-old National Air Traffic Services (Nats) system at 6am meant scores of flights were cancelled and others were badly delayed.

Although the system was up and running again within an hour, it was several more hours before some passengers could get away on flights and delays continued throughout the day.

Nats said the fault occurred when it was doing overnight tests on its computer system at its centre in West Drayton, West London.

Huge queues built up at check-in desks at airports around the country and many services at Heathrow were delayed up to two hours.

Among those held up at Heathrow was former Chancellor of the Exchequer Kenneth Clarke who was trying to get to Milan.

Newcastle and Teesside airports were similarly affected leading to frustrations for grounded holidaymakers.

Chris Stalker, 37, a joiner from Durham City, was due to fly to Orlando, Florida, from Newcastle Airport with his wife and children, but found that his 12.50pm flight had been delayed almost two hours.

He said: "We've got two kids aged eight and four and it's a question of keeping them occupied while we wait."

Carl Bevan, duty manager at Newcastle Airport, said: "We received a phone call at about 6.30am and had to stop certain flights taking off.

"The first round of scheduled flights from this morning were cancelled which had a knock-on affect all day because of extra pressure on air space."

By about lunchtime at Teesside Airport two flights had been cancelled and six delayed.

The longest delay was for a flight from Palma, which was due into Teesside at 2pm, but was more than two and-a-half hours late.

Airport spokesman John Waiting said: "It was very disruptive first thing, but by early afternoon we were pretty much getting back to our normal schedules."

The air traffic control breakdown was criticised by Tory leader Michael Howard who said it was "yet another example of Government incompetence".

Transport Secretary Alistair Darling said money was now being invested in Nats and delays caused by air traffic control had come down dramatically over the past few years.

Although Nats has a new £62m centre at Swanwick, near Southampton, both the West Drayton and Swanwick controllers rely on flight data information from the West Drayton computer system, whose software dates back to the 1970s.

It was this system that failed in similar fashion in June 2000 leading to flight chaos even worse than that experienced yesterday.

With flight details having to be typed by hand during the shutdown, Nats chiefs insisted that passenger safety had not been compromised.

Nats chief executive Richard Everitt admitted the system needed upgrading and said he apologised to all those passengers affected.