Passengers have been told to expect delays of up to 12 hours after air traffic controllers across the UK experienced a technical fault.

In an updated statement this afternoon, the National Air Traffic Services (NATS) said the “technical issue” affecting its flight planning system had been “identified and remedied”, but travellers continued to face disruption.

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“We are now working closely with airlines and airports to manage the flights affected as efficiently as possible,” NATS said.

“Our engineers will be carefully monitoring the system’s performance as we return to normal operations.

“The flight planning issue affected the system’s ability to automatically process flight plans, meaning that flight plans had to be processed manually which cannot be done at the same volume, hence the requirement for traffic flow restrictions.

“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.”

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NATS did not give an estimate of how long it would take to fix the problem, or what had caused it.

Transport Secretary Mark Harper said the “technical issue” affecting the National Air Traffic Services “has now been resolved”.

On a post on X, formerly known as Twitter, he said that he and aviation minister Charlotte Vere were “continuing to work with NATS to help them manage affected flights and support passengers”.

“All passengers should still contact their airline for specific flight information.”

European air traffic authority Eurocontrol and Irish air traffic controllers AirNav Ireland have both warned of significant delays across Europe.

The Liberal Democrats have called on the government to hold an urgent COBRA meeting, while the Labour‘s shadow transport secretary said the fault was “extremely concerning”.

Some 3,049 flights were due to depart from UK airports today and another 3,054 flights were scheduled to arrive – with around one million passengers on board.

Travellers have been told to expect severe delays of up to 12 hours.

BBC presenter Gabby Logan said she had been caught up by the issue.

She posted on X, formerly known as Twitter: “On a plane on the runway at Budapest airport. After almost three weeks away from home I am hours from hugging my family.

“And have just been told UK airspace is shut. We could be here for 12 hours. So we sit on the plane and wait.”

Sky’s science correspondent Thomas Moore is one of the passengers stuck on a British Airways flight at Heathrow after flying back from San Francisco overnight.

Speaking from the plane, he said the aircraft actually landed ahead of the schedule – but since then they have been stuck on the tarmac.

“The pilots told us that we are in a queue for a gate because all the aircraft giving priority to land can’t get away, so everything is stacking up now,” he said.

“We have an update saying that they’re trying to find space for all the aircraft that are coming in and having to wait, having to queue, because this is going to have a big impact.

“There are planes taking off, but what we are being told is that various aspects of computerised systems used by air traffic control aren’t talking to each to other, so everything is having to be done manually.

“That means things are taking a lot longer than they would be.

“Normally this would be one of the busiest runways in the world, but it is looking very, very quiet.”

Sky News producer Georgia Ziebart, who is stuck on a plane in Palma, Majorca that is set for London Gatwick, said passengers have been told all planes that were in the air at the time the systems went down have been diverted to other countries.

She said: “We’re on the tarmac in Palma, Majorca – we got on the plane an hour ago and shortly after we got on the plane, the pilot made an announcement to say it doesn’t look like we’ll be leaving for a while because there are issues with air traffic control across the whole of the UK.

“We’ve been sat on the plane now for about an hour, still haven’t moved, still haven’t had much information. But staff just said there’s no point in us moving because we can’t actually go anywhere.

“There are people who have been sleeping at the airport since yesterday so it’s completely at capacity inside as well.

“There’s a lot of children on board here, a lot of babies. It’s a three-hour flight. I haven’t got any food. They’ve come around and offered water to everyone but that’s it at the moment.”

Airports and airlines have warned customers that they may experience delays and urged those travelling today to check their flight details.

Ryanair and Aer Lingus were the first airlines to confirm several flight cancellations to and from Dublin and Cork airports.

British Airways said it was “working closely with NATS to understand the impact of a technical issue that is affecting UK airspace, and will keep our customers up to date with the latest information”.

The Eurostar said it would add an extra train from Paris to London at 8.43pm this evening after the airline disruption.