Air traffic authority says a technical issue affected its system’s ability to automatically process flight plans.

NATS had earlier had to restrict the flow of aircraft after the issue affected its system’s ability to automatically process flight plans, with airlines and airports warning of delays and cancellations.

“We have identified and remedied the technical issue affecting our flight planning system this morning. We are now working closely with airlines and airports to manage the flights affected as efficiently as possible,” NATS said in a statement later on Monday.

“The flight planning issue affected the system’s ability to automatically process flight plans, meaning that flight plans had to be processed manually which cannot be done at the same volume, hence the requirement for traffic flow restrictions.”

The UK’s Secretary of State for Transport Mark Harper said while the issue was resolved, flights were still “unfortunately affected”.

Earlier, Irish air traffic control provider AirNav Ireland said the issue, which struck during a public holiday in parts of Britain, was resulting in “significant delays for flights across Europe that are travelling to, from or through UK airspace”.

A spokesperson for London Heathrow, the busiest hub in western Europe, said schedules would remain significantly disrupted for the rest of the day.

British Airways said its flights were being severely disrupted and it had made “significant changes” to its schedule, while other airlines also said some flights to and from the UK would be delayed or cancelled.

Manchester Airport, London Stansted and London Gatwick were among the many UK airports that warned of delays and cancellations, while Dublin Airport in the Republic of Ireland said the issue had resulted in delays and cancellations to some flights into and out of the Irish capital.

Many passengers took to social media to say they were stuck on planes on the tarmac waiting to take off, or being held in airport buildings in Spain, Portugal, Greece, Israel and elsewhere on what is a traditionally busy travel day as the school holidays draw to a close.

Passenger Mike Woolridge posted from Amsterdam, saying that “pretty much every flight” to the UK was cancelled.

“Sending positive energy to the NATS tech team …”, he posted on X, formerly known as Twitter.

Current situation at @Schiphol, pretty much every single flight headed to the UK cancelled 😬 Sending positive energy to the @NATS tech team and controllers right now… won’t be the easiest shift! #airtrafficcontrol pic.twitter.com/yRycyQglID

— Mike Wooldridge (@mdw1989) August 28, 2023