AIR passengers have been warned to expect “significant delays” after a UK air traffic control failure.

The National Air Traffic Services (NATS), the country’s leading provider of air traffic control services, said it has applied traffic flow restrictions on Monday to maintain safety following a technical issue.

It added in an update on Monday that controllers are having to input flight plans manually due to a fault with its systems.

NATS have since said it has “identified and remedied” the technical issue.

The Prime Minister had been urged to hold an urgent COBRA meeting to discuss the disruption to the systems. Sunak has not publicly commented on the issue yet. 

It is understood passengers boarding flights both to and from the UK have been told of the fault as many face hug waits for flights. 

NATS previously apologised for the disruption, which is causing significant delays at UK airports.

In a statement, NATS said: “This morning’s technical issue is affecting our ability to automatically process flight plans.

“Until our engineers have resolved this, flight plans are being input manually which means we cannot process them at the same volume, hence we have applied traffic flow restrictions.

“Our technical experts are looking at all possible solutions to rectify this as quickly as possible.

“Our priority is ensuring every flight in the UK remains safe and doing everything we can to minimise the impact.

“Please contact your airline for information on how this may affect your flight. We are sincerely sorry for the disruption this is causing.”

An earlier statement from NATS said: “We are currently experiencing a technical issue and have applied traffic flow restrictions to maintain safety.

“Engineers are working to find and fix the fault. We apologise for any inconvenience this may cause.”

Loganair warned customers on X, formally known as Twitter, that flights may be subject to delays due to the outage.

In a statement, the Glasgow-based airline said: “There has been a network-wide failure of UK air traffic control computer systems this morning.

“Although we are hopeful of being able to operate most intra-Scotland flights on the basis of local co-ordination and with a minimum of disruption, north-south and international flights maybe subject to delays.

“If you are flying with us today, please check our website for the latest information about your flight before setting off for the airport.”

Leading travel journalist Simon Calder warned passengers: "If you're booked to fly into or out of the UK be prepared for serious disruption.

"I'm afraid experience tells us something like this is not going to end quickly, it's going to be very messy."

A lot of planes will end up touching down in places such as Amsterdam or Paris instead of their UK destinations, he suggested.

Calder added there will be "many thousands of people waking up tomorrow somewhere they don't want to be".

He predicted the situation will cost airlines "millions of pounds".

Irish minister of state for transport Jack Chambers has warned of a “major” knock-on impact on flights to and from Ireland as a consequence of the UK air traffic control fault.

“There’s traffic flow restrictions have been introduced to maintain safety in the sky and it will have significant impacts on passengers flying in and out of Dublin, and there are multiple slot restrictions,” Mr Chambers told RTE Radio One.

“So, we’d encourage customers to contact their airline for an update but it will have a major impact on Irish travel because, obviously, the nature and the proximity to UK space.

“There will be an impact and delays of several hours for many passengers, and we’d encourage them to contact their airlines.”

The Liberal Democrats have asked Rishi Sunak to "get a grip" on the failure urgently by holding an urgent COBRA meeting. 

COBRA meetings are usually called in response to instances of national or regional crisis, or during events abroad which have major implications for the UK.  

"Rishi Sunak and his ministers need to get a grip on this issue urgently and hold a COBRA meeting," said Liberal Democrat transport spokesperson Wera Hobhouse. 

"Millions of holidaymakers could be facing huge disruption in the coming days due to this fault, and we can't risk this government being missing in action yet again.

"Brits need to know that the government is doing all it can to make sure people aren't hit with major delays and disruptions in the coming days." 

A Heathrow spokesman said: “As a result of national airspace issues there is disruption to flights across the UK. Passengers are advised to check with their airline for the latest information.

“We are working closely with NATS and other airport partners to minimise the impact this has on passengers.”

Meanwhile at Stansted, Ryanair passengers told press they had been told to wait at their gate until further notice.

British Airways said in a statement: “We are 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.”

Tui warned of “significant delays”.

In a reply to a passenger asking if their flight on Tuesday is likely to be delayed, Tui tweeted: “Due to an Air Traffic Control outage across UK airports, we expect that this may cause significant delays to some of our flights.

“We would like to advise customers to monitor the departure boards or your emails for further updates.

“We apologise for any inconvenience caused.”

Michele Robson, who used to work in air traffic control, said that it was “unusual” for failures to last this long.

She told BBC Radio 4’s World At One programme: “There was a flight planning system failure this morning which affected both centres in the UK.”

Speaking from Jersey Airport while waiting to fly to London, she said: “Now they have enough data for four hours for controllers to work normally. After that point, they have to go manual which means that they work at a much slower rate so they can handle far less aircraft.

“So it looks like there’s been what they would call a zero rate put on, where it means that no aircraft can take off inbound to the UK or probably outbound. It would generally be them trying to land things that were already in the air.

“So at the moment, we’re just sitting here with no definite takeoff time.”

She said failures normally “only last a couple of hours”.

“It’s unusual for it to be off for this amount of time. So nobody really knows at this point how long it’s going to take.”

BBC presenter Gabby Logan said she had been caught up in the delays.

She tweeted: “On a plane on the runway at Budapest airport. After almost 3 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.”

In a statement, NATS said: “We have identified and remedied the technical issue affecting our flight planning system this morning.

“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.

“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.”