The UK's air traffic control provider Nats disclosed a technical issue at around 1.45pm on Tuesday (8 September).

Sky News reported up to 10 airports in the UK and Ireland had been affected; others include Stansted and East Midlands, while Edinburgh warned of potential disruption to services.

Shortly before 3.30pm, Nats confirmed it had identified an issue with its flight processing system, adding engineers were on site working to resolve the issue and "resume normal operations as quickly as possible".

"We recognise the ongoing disruption to travel, for which we sincerely apologise," it said. "Flights are still departing and airspace is open, but recovery will take some time."

Nats said a fix had been implemented by 4.40pm and that its flight system was "starting to recover". However, three hours later, it added this recovery was taking "longer than hoped" despite the issue having been fixed.

"We are operating normally and working as hard as possible to clear the backlog of flights," said Nats. "We are truly sorry for the ongoing flight disruption. We know this is hugely frustrating and apologise unreservedly."

A final update, issued at 10.10pm, read: "Work is continuing to assist airlines and airports recover from today’s disruption. This has been a very complex recovery and has created difficulties for the whole aviation network, from which it will take time to recover."

It's the latest in a series of major UK ATC outages in recent years, prompting renewed questions about whether the UK's ATC provision is fit for purpose, and further calls for Nats Chief Executive Martin Rolfe to resign. Asked by the BBC whether he was considering his position, he said there would be "lots of time for that later".

Rolfe added it was not the same system that failed over the August 2023 bank holiday weekend.

Transport Secretary Heidi Alexander said she was made aware of the issue shortly after the fault was identified. "Technicians have identified the issue and are fixing it as we speak," she said. "I know this will be frustrating for passengers and I'm sorry. Please check with your airline for latest advice."

She later added: Pleased Nats have fixed the issue, and huge thanks to those working to get people moving. It will take time to fully resume flights, so continue to check with airlines. I am seeking assurances that lessons will be learned and systems that support aviation are up to the job."

The BBC reports Alexander has summoned Rolfe for a meeting on Wednesday to investigate the disruption and Nats' response. She is also expected to rule out the fault being caused by a cyber attack.

According to aviation analytics firm Cirium, nearly 2,000 flights have so far been affected by the disruption. More than 1,750 of the 5,800 flights scheduled to arrive into and depart UK airports on Tuesday were cancelled. And by 5am on Wednesday, 153 flights – 55 departures and 98 arrivals – had been cancelled.

EasyJet had the most departures – 601 – scheduled for Tuesday, of which 219 (36.4%) were cancelled or did not fly. Of those airlines scheduled to operate more than 100 departures on Tuesday, British Airways had the highest cancellation or no-fly rate of 44.4%. Of its 507 scheduled departures, 225 were cancelled or did not fly.

At Heathrow, 241 of the 661 departures scheduled for Tuesday were cancelled or did not fly (45.4%), the highest rate of those airports affected.

Heathrow said: "Following yesterday’s technical issue affecting Nats air traffic control, Heathrow’s operations are recovering. Flights are operating today (Wednesday), however some knock-on disruption is expected as airlines reposition aircraft and crew.

"Passengers are advised to check the latest status of their flight directly with their airline and to only travel to Heathrow if their flight is confirmed as operating today. We apologise to passengers affected by the disruption.

"Additional colleagues are available across our terminals to provide support, and we are working closely with NATS and our airline partners to return operations to normal as quickly as possible.

Luke Petherbridge, Abta's Director of Public Affairs, said people's rights will vary depending on whether they booked their flight separately or as part of a package. "Abta members will be supporting those booked with them, to help make alternative arrangements, and we have advice on abta.com to help people understand their rights.

“While the immediate priority is supporting customers, as this isn’t the first Nats outage to cause widespread disruption, the industry and the public will want answers as to what has gone wrong, what lessons are being learned, and how the system will be made more resilient to avoid this happening again."