Some 38 flights were cancelled at Heathrow Airport this morning after chaos at UK airports last night due to a technical issue with the air traffic control centre.
While air traffic control company Nats declared its systems are back to full operational capacity, the flight mayhem at some of the UK's busiest thoroughfares could still be a reality for some passengers.
Dozens of flights were cancelled and many others delayed after a computer failure at Nats' company headquarters at Swanwick, Hampshire, yesterday afternoon.
A spokesman for Heathrow said 38 flights are cancelled before 9.30am today "as a knock on from yesterday".
Last night passengers in Ireland were advised to consult their airline or airline's website before coming to the airport but no major delays are reported this morning.
Nats said at about 8pm last night: "Following a technical fault with the flight data system used by air traffic controllers at Swanwick, Nats can confirm that the system has been restored to full operational capability and a thorough investigation is continuing to identify the root cause.
"Although operational restrictions applied during the failure have been lifted, it will take time for flight operations across the UK to fully recover so passengers should contact their airline for the status of their flight. We apologise for the impact that this issue has had, and the delays and inconvenience caused."
The company has ruled out a power outage as the source of the glitch at Nats' state-of-the-art £700m centre.
Airports as far north as Aberdeen and Edinburgh were affected by the computer problem.
Other airports that reported delays yesterday afternoon included Manchester, Stansted and Luton.
Gatwick Airport said yesterday evening: "Some cancellations should be expected and passengers are advised to contact their airline for the latest flight information.
At Heathrow, a spokesman said yesterday there had been 70 cancellations out of about 1,300 scheduled flights. "They're coming back to normal now," he said.
The airport put extra staff on duty and were due to be open later than usual to try to get stranded passengers in the air.
Birmingham Airport had experienced delays but reported its air traffic was back to normal by 8pm.
Transport Secretary Patrick McLoughlin described the disruption as unacceptable.
He said: "Any disruption to our aviation system is a matter of the utmost concern, especially at this time of year in the run up to the holiday season.
"Disruption on this scale is simply unacceptable and I have asked Nats for a full explanation of this evening's incident. I also want to know what steps will be taken to prevent this happening again."
