Airline passengers have been cautioned about potential extended flight disruptions as a technical breakdown in the UK's air traffic control system left hundreds of thousands of travelers stranded on Monday.

Returning holidaymakers and those intending to depart from UK airports encountered flight cancellations and delays of up to 12 hours due to a widespread computer failure that affected both outgoing and incoming flights.

The technical breakdown in the country’s air traffic control system led to a holiday weekend filled with frustration as 500 flights were canceled and numerous others faced significant delays, according to British media.

Britain’s National Air Traffic Services (NATS) said it was dealing with the issue.

"We are now working closely with airlines and airports to manage the flights affected as efficiently as possible. Our engineers will be carefully monitoring the system’s performance as we return to normal operations.

"Our priority is always to ensure that every flight in the UK remains safe, and we are sincerely sorry for the disruption this is causing. Please contact your airline for information on how this may affect your flight," it added.

British Airways announced that passengers with Monday or Tuesday travel plans could reschedule their flights at no extra cost.

“Like all airlines using UK airspace, our flights have been severely disrupted…While NATS has now resolved the issue, it has created significant and unavoidable delays and cancellations. We’re working as hard as possible to get customers whose flights have been affected on their way again and have apologized for the huge inconvenience caused,” it said on the social media platform X, formerly known as Twitter.

The travel operator Tui also urged its customers to expect significant delays to some of its flights. (Anadolu agency)

•A Heathrow spokesperson on Monday said passengers should only travel to the airport if their flights were confirmed as operating.