Thousands of travellers had been stranded by the problem, which caused lengthy hold-ups at airports around the country.

It's just been a complete and utter mess

Toby Nicol, Easyjet

The problem began at the air traffic control centre in Swanwick, Hampshire, early on Friday morning.

Although it was fixed five hours later, delays continued until the backlog of flights could be cleared by airlines.

Almost all UK airports, including Scottish airports, suffered delays - with waits of five hours reported at Luton and Newcastle.

British Airways had to cancel 87 flights on Friday, and many travellers had to sleep overnight at Heathrow and elsewhere.

Knock-on problems

Toby Nicol, from budget airline Easyjet, said it was forced to refund passengers without any hope of receiving compensation itself.

He told BBC Radio 5 Live: "It's just been a complete and utter mess."

Air traffic controllers at Swanwick had to halve the number of aircraft normally in the skies because only half of the control positions were working at full capacity on Friday morning.

Services were further affected by an air traffic control problem in Brussels, which has delayed the recovery of flights out of Gatwick and Heathrow in particular.

Frustrated

Nats said the problem began after a regular monthly computer upgrade at Swanwick, which controls most of the airspace across England and Wales.

Nats chief executive Richard Everitt insisted safety had not been compromised.

It is the third time in two months flights have been delayed by air traffic control system problems.

Air traffic control problems 2002

Jan: �623m Swanwick centre opens six years late Feb: Nats given a �60m loan for losses since 11 Sep March: West Drayton control centre hitch disrupts flights 10 April: More disruption from West Drayton control centre 17 May: Computer failure at Swanwick causes delays of up to 6hrs

Flights were delayed for up to two hours last month when a computer problem hit West Drayton air traffic control centre near Heathrow.

A similar problem at West Drayton on 27 March led to severe disruption to pre-Easter services.

Passengers said they were very frustrated by the delays, especially at the lack of information.

Dan and Helen Stewart were hoping to fly from Heathrow to Finland on business, but staff were unable to tell them when their flight would leave.

"You just never know when you're going to get there, so you don't know how to call and tell anybody at the other end when you're going to show up," said Mr Stewart.