As hundreds of thousands of passengers were left stranded on Monday due to a technical malfunction in the UK's air traffic control system, airline customers have been warned about potential lengthy flight delays.

A severe computer malfunction that affected both outbound and incoming flights resulted in flight cancellations and delays of up to 12 hours for travelers returning from vacations and those planning to leave from UK airports.

According to British media, the country's air traffic control system malfunctioned technically, causing 500 flights to be canceled and a great number of others to have major delays over the holiday weekend.

The problem was being addressed, according to the National Air Traffic Services (NATS) of Britain.

"We are currently coordinating closely with airports and airlines to manage the impacted flights as effectively as we can. As we resume regular operations, our engineers will closely monitor the system's performance.

"Our top concern is always ensuring the safety of every flight in the UK, and we truly apologize for the inconvenience this is creating. For details on how this can effect your flight, kindly contact your airline, it was added.

British Airways advised customers with travel reservations for Monday or Tuesday to reschedule their flights at no additional cost.

"Our flights have been badly interrupted, just like all airlines utilizing UK airspace…Despite the fact that NATS has since fixed the problem, it caused considerable and unforeseen delays and cancellations. We apologize for the extreme inconvenience caused and are making every effort to get clients whose flights have been impacted on their way once more, the company said on the social media site X, formerly known as Twitter.

Additionally, the travel agency Tui warned its clients to anticipate substantial delays on a few of its flights.