LONDON: The British government was working with airlines on Tuesday to help ensure passengers stranded in airports across Europe can get home after an air traffic control glitch caused widespread disruption to flights that is expected to last for days.

More than 1,500 flights were cancelled on Monday - a public holiday in parts of Britain, and one of the busiest travel days as the school holidays draw to close - when air traffic controllers were forced to switch to manual systems due to a technical problem.

That left thousands of passengers stuck at airports in Europe and further afield.

"We were stuck in the airport for about seven or eight hours yesterday. We were left high and dry," said Maria Ball, a holidaymaker from Liverpool, in northwest England.

She said she ended up at Paris' Charles De Gaulle airport, having finally found a flight to Edinburgh, and was then facing a four-hour journey in a hire car to get home when she lands.

Martin Rolfe, CEO of Britain's National Air Traffic Services (NATS), apologised for the technical failure on Tuesday, and said initial investigations into the problem show it relates to some of the flight data it received.

"Our systems, both primary and the back-ups, responded by suspending automatic processing to ensure that no incorrect safety-related information could be presented to an air traffic controller or impact the rest of the air traffic system," Rolfe said in a statement.

Mark Harper, the transport secretary, warned it would take days to resolve the issues, even though the fault was fixed after a few hours on Monday. The cancellations hit airline schedules, meaning planes and crews were out of place.

Prime Minister Rishi Sunak said he understood people were frustrated.

"The transport secretary is in constant dialogue with all the industry participants," Sunak said. "He will be talking to airlines specifically later today and making sure that they support passengers to get home as quickly as possible."

Harper chaired a meeting on Tuesday with NATS, the Civil Aviation Authority (CAA), airlines, airports, trade bodies and Border Force. He said the government will be reviewing a report from NATS in the coming days.

Harper said government officials did not believe the technical problem, the first on this scale for a decade, was the result of a cyberattack.

Aviation analytics firm Cirium said 790 flights departing British airports were cancelled and 785 flights due to arrive were cancelled on Monday, meaning just over a quarter of all flights into or out of the country were affected.

Ryanair, Europe's biggest airline, would be operating a normal schedule by Wednesday, said boss Michael O'Leary, as he criticised how NATS had handled the situation.

"We still haven't had an explanation from them, what exactly caused this failure yesterday and where were their back-up systems," O'Leary said in a video posted on X, formerly known as Twitter.

British Airways said it was working hard "to get back on track" and had offered passengers flying short-haul routes to change their flight dates free of charge.

EasyJet said that the knock-on impact meant some flights were cancelled on Tuesday morning.

Heathrow Airport, Britain's busiest hub, told passengers to contact their airline before travelling to the airport on Tuesday.