Flight delays are expected to continue on Wednesday after an air traffic control problem cancelled hundreds of flights across the UK.

Tens of thousands of passengers were affected by the disruption, and tracking website FlightRadar24 said up to 1,000 flights were cancelled after a glitch affecting air traffic control provider NATS.

Its boss Martin Rolfe apologised, telling the BBC there would be a full investigation into what had gone wrong, after Nats said resolving the issue had taken "longer than hoped".

The BBC understands Transport Secretary Heidi Alexander has summoned Rolfe to a meeting on Wednesday to answer questions about the disruption and response.

She is also expected to tell MPs that a cyber attack was "categorically" not the cause of the fault.

With few aircraft able to take off, it is understood landings were restricted, leading to some flights being unable to depart overseas airports.

The fault was widespread across the UK, and beyond, with airports in Scotland and Ireland also reporting disruption. EasyJet made 200 cancellations and British Airways more than 100.

It is not the first time disruption has blighted Nats' control system. Ryanair and Wizz Air called for an overhaul of the organisation, with Wizz Air saying Nats was "not fit for purpose" in its current form.

When asked whether he was considering his position, Rolfe said there would be "lots of time for that later" but his focus now was on making sure the problem was solved.

Europe's busiest airline, Ryanair, reported on Tuesday that more than 65,000 passengers had been delayed by up to eight hours.

At Heathrow, one of the busiest airports in Europe,departures were initially paused around lunchtime. Traffic then resumed, before facing further disruption in the afternoon.

It is understood the airport ran out of space for incoming flights during the afternoon because planes had not been departing.

Thirteen Heathrow-bound flights were diverted to other airports in the UK and Europe.

Passengers have been advised to contact their airlines to check the status of their flights.

British Airways said in a statement that it was anticipating knock-on effects.

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

"We're doing everything we can to keep our customers updated and make arrangements for them to continue their journeys.

"We ask customers whose flights have been cancelled not to travel to the airport and to bear with us if they're trying to get in touch, as our call centres are incredibly busy at the moment."

Airports across the UK said they were experiencing cancellations and delays and advised people to check their flight details before travelling.

According to FlightRadar, the worst affected airports were Heathrow, Gatwick, Manchester and Birmingham.

Ryanair said affected passengers would be notified.

Phil White from Bexhill told BBC Your Voice that his flight to Lanzarote boarded on time but he was left sitting on the tarmac at Gatwick for hours.

"We've been told the radar is down and we can't take off," Phil said.

"It's comfortable enough but the pilots been on every 20 minutes saying they are waiting for information from air traffic control and when he finds anything out he will let us know."

Knock-on effects as backlog builds

Even ifNats has resolvedthe issue with its flight processing system, the disruption is likely to persist due to backlogs.

Rolfe said the issue was in Nats' flight data processing system. He said it was not the same system that failed during an incident in 2023 over the August Bank Holiday weekend.

Although the technical issue affected departures, arrivals were also hit as space on the ground became increasingly restricted.

Transport Secretary Heidi Alexander said that "it will take time to fully resume flights, so continue to check with airlines".

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

According to Nats, the flight processing system processes flight plans and other operational information used by air traffic controllers to manage air traffic.

The system continually updates flight information as aircraft progress through UK airspace, helping controllers maintain a safe and orderly flow of traffic.

Chloe Davis,18, from Cambridgeshire was left sitting on a Virgin plane at Heathrow waiting to fly to Orlando.

She told BBC Your Voice that she had been due to depart at 13:40 BST.

"I'm not concerned, I would just like to know what's going on," she said.

"There [are] planes parked up on the taxi way because there's no gates for them to go to."