There are widespread delays at several airports after UK airspace was hit by a network-wide failure for air traffic control systems.
All major airlines are affected with advice for travellers to check on possible delays before heading to the airport.
More than a million people were due to fly into or out of the UK on Bank Holiday Monday, one of the busiest travel days of the year.
Data from aviation analytics firm Cirium revealed that hundreds of flights were cancelled.
A total of 232 flights departing the UK, the equivalent to eight per cent of all departures, have been scrapped.
Meanhile 271 flights due to arrive on the UK have been cancelled which equates to almost one in ten of the total.
British Airways said they 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.”
In a statement, National Air Traffic Services (NATS), which provides air traffic control services in the UK, said they had “identified and remedied” the technical issue affecting air traffic control systems, as passengers face major delays at airports across the UK.
But the system being down for hours will have an impact on hundreds of flights with air traffic controllers dealing with a huge backlog.
An earlier statement 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.”
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.”
EasyJet is offering customers on cancelled flights a refund or a free flight transfer due to air traffic disruption.
The airline said in a statement: “We have been advised of an air traffic control systems failure affecting UK airspace, which is currently causing disruption to flying programmes for airlines operating to and from the UK.
“We are providing customers on cancelled flights with the option to transfer their flight free of charge or receive a refund and recommend that all passengers flying with us today, regardless of their destination.”
It also apologised for the inconvenience, and said it is “doing everything possible to minimise the impact of the disruption”.
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.”
Gatwick Airport said on Monday afternoon that planes there are still landing and taking off.
Flights are continuing to take off across the UK at reduced levels and UK airspace is not closed.
According to the latest data, 3,049 flights were due to leave the UK today with 540,000 customers seated.
A further 3,054 flights were scheduled to arrive into UK airports on Monday bringing in an additional 543,000 passengers.
Ryanair passengers waiting at Stansted Airport in Essex said there were cheers when two flights to Copenhagen and Paphos were announced for boarding amid delays caused by a UK air traffic control failure.
They said that they had heard airlines cancel around five flights while they had been waiting at the gate.
Posting online, an easyJet passenger wrote: “Just informed by easyJet that my flight tonight is likely to be delayed by nearly 7 hours.
“Manchester to Prague. Apparently air traffic control system issue.”
BA passengers were also facing huge delays, with one saying: “Currently being told that we will be sat on the tarmac for 7 hours in Milan!”
TV presenter Gabby Logan was also hit by the delays.
She said: “On a plane on the runway at Budapest airport. After almost 3 weeks away from home I am hours from hugging my family.
“And I have just been told that the UK airspace is shut. We could be here for 12 hours. So we sit on the plane and wait.”
The Liberal Democrats have called on the Prime Minister to convene a Cobra meeting.
Transport spokesperson Wera Hobhouse said: “Rishi Sunak and his ministers need to get a grip on this issue urgently and hold a Cobra meeting.
“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.”
Meanwhile Labour’s shadow transport secretary Louise Haigh said news of delays to flights in and out of the UK was “extremely concerning” for air passengers.
In a statement on X, formally known as Twitter, she said: “Extremely concerning for passengers travelling in and out of the UK on one of the busiest days of the year.
“UK airspace is not closed but significant delays expected thanks to a technical fault.
“Surprised not to see our Transport Secretary make a statement yet.”
Tui has warned of “significant delays” due to the air traffic control outage.
In a reply to a passenger asking if their flight on Tuesday morning is likely to be delayed, Tui posted on X, formerly known as Twitter, saying: “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.”
Ryanair and Aer Lingus have cancelled a number of flights out of and returning to Dublin Airport as a result of the air traffic control issues.
Services are also understood to be impacted at Cork.
The Aer Lingus airline said: “Due to a failure of the UK air traffic control flight planning systems, which is outside of Aer Lingus’ control, there are severe restrictions on all flights into the UK and flying over UK airspace today.
“We would ask you to check the status of your flight before coming to the airport today as delays and cancellations are likely.”
Ryanair said: “Due to another UK ATC failure, Ryanair will be forced to delay/cancel a number of flights to/from the UK today, Aug 28.
“All affected passengers will be notified of their options to change flights (free of charge) to another Ryanair flight or receive a full refund.
“We sincerely apologise for this UK ATC failure which is beyond Ryanair’s control and is affecting all airlines operating to/from the UK.”
Shannon Airport said the forced restriction of aircraft flow has resulted in the cancellation of the outbound (FR1182) and inbound (FR1183) Ryanair Gatwick service.
A spokesperson for Shannon Airport has advised all passengers due to travel from Shannon to check the status of their flight with their airline in advance of travelling.
Have you been impacted by the disruption? Email firstname.lastname@example.org