Hundreds of thousands of air passengers had flights delayed or cancelled after another UK air traffic control technical glitch kept planes grounded for hours on Tuesday.

Airlines demanded action after a "technical issue" at the air traffic control services provider Nats caused the third large-scale stoppage in just over three years.

At least 600 flights in and out of the UK were reported cancelled by late Tuesday afternoon in an incident that started at about 1pm and affected departing flights at many of Britain's biggest airports, including Heathrow and Gatwick.

By the time Nats said it had identified and implemented a fix to restart its flight processing system almost four hours later, most flights scheduled to depart from the London airports and others were yet to take off. The disruption had spread to include incoming flights to much of southern England.

Cancellations and delays were continuing well into Tuesday evening, and British Airways said disruption would affect operations through Wednesday at least, with passengers offered free rebooking until Friday.

Ryanair said more than 65,000 passengers had been delayed and 50 flights cancelled. The knock-on effects hit flights across Europe, according to easyJet. Eurocontrol said some inbound flights were being held at airports abroad, with disruption likely until the evening.

All London airports, as well as Manchester and Birmingham, were among the most directly affected. Flights to and from other airports around the UK, including Edinburgh and Belfast, were also disrupted.

According to the flight monitoring website FlightRadar24, easyJet had 137 flights cancelled, British Airways 111, KLM 26, Eurowings 22 and Ryanair 21 by 5pm.

Nats initially announced at 1.46pm that it was "investigating a technical issue which is causing some disruption to flight departures". It later identified the problem in its flight processing system, and announced at 4.40pm that it had implemented a fix.

A spokesperson said the fault was not the same as the ones that caused previous outages and mass disruption in 2023 and 2025.

They said the system was only "starting to recover".

"We are continuing to work closely with our airline and airport customers on recovery," they said. "We apologise sincerely for the disruption to people's journeys today and they should continue to check with their airline."

The chief executive of Nats, Martin Rolfe, expressed his "huge sympathies to everyone who has been caught up in today's disruption".

"We absolutely take responsibility for this," he told Sky News.

"We never want this sort of thing to happen. I completely understand how frustrating it is for passengers."

He claims, however, "these things are relatively rare".

"We resolved it to get back to our systems operating normally," he added. "But of course, there's a huge amount of disruption that's now built up in the system.

"We're working very closely now with airlines and airports to try to work through the night to make sure that we can get as many people travelling as possible."

The air traffic control problems follow an "isolated event" a year ago which caused widespread disruption, although it so far appears less severe than the full grounding of flights in August 2023, which prompted a parliamentary inquiry.

However, British Airways said that "the severity of the issue means there will be a significant knock-on impact for customers and colleagues".

"We were forced to cancel or divert more than 100 flights on Tuesday afternoon, inconveniencing tens of thousands of customers," a spokesperson said.

"This incident was entirely out of our control and incredibly frustrating for our customers and colleagues, with aircraft and crews ending up out of place."

Heathrow originally said only departures had been affected, but a later statement confirmed that the issue was "impacting arriving and departing flights across UK airports".

Airlines renewed calls for Nats to be overhauled after the third incident ascribed to its systems in as many years.

Ryanair repeated its calls for Rolfe to resign. The Irish airline's chief operating officer, Neal McMahon, said: "Families travelling on holiday, people travelling for work and thousands of visitors to the UK have once again paid the price for Nats' abhorrent failure."

He said the government should "stop making excuses for repeated Nats failures and appoint a new leader capable of running the UK ATC system".

Wizz Air said: "A critical national infrastructure provider should not repeatedly bring the aviation system to a standstill. Nats is simply not fit for purpose in its current form."

The transport secretary, Heidi Alexander, said: "I'm aware of a technical issue impacting flights at airports including Heathrow and Gatwick. Technicians have identified the issue and are fixing it as we speak. I know this will be frustrating for passengers and I'm sorry.

"I am seeking assurances that lessons will be learned and systems that support aviation are up to the job."