Widespread flight disruption that left thousands of passengers stranded was caused by incoming flight data, air traffic control bosses say.

National Air Traffic Services said a flight plan that its systems could not process was behind Monday’s technical problem.

The fault saw passengers stranded abroad and in the UK, having to find alternative routes home.

Passengers have been warned to expect continued knock-on disruption.

One passenger told BBC News she and her young children slept on the floor of an airport after their flight was axed.

Nats confirmed there were no signs the failure was caused by a cyber-attack. The incident will be investigated by the Civil Aviation Authority (CAA).

Nats chief executive Martin Rolfe said: “Initial investigations into the problem show it relates to some of the flight data we received.

“Our systems, both primary and the back-ups, responded by suspending automatic processing to ensure that no incorrect safety-related information could be presented to an air traffic controller or impact the rest of the air traffic system.”

He later described the issue as “incredibly rare”, saying he was confident the situation would not arise again.

“We understand the way the system didn’t handle the data… the way it failed, if you like.

“So we have put in place, already, procedures to make sure if that happens again, we can resolve it very, very quickly.”

Asked about reports that a flight plan submitted by a French airline could be behind the problem, Mr Rolfe said he “wouldn’t want to speculate at this point”.

He said Nats was working with the CCA to provide a preliminary report to the transport secretary on Monday – and that the report’s conclusion would be made public.

The Department of Transport said it had approved night flying to all UK airports it regulates to alleviate the backlog in UK flights.

It follows a meeting of Nats, the CAA, airlines, airports, trade bodies and Border Force, chaired by Transport Secretary Mark Harper.

Speaking after the meeting, Mr Harper warned again that the knock-on effects of Monday’s disruption are likely to continue over the coming days, and said passengers due to travel should check with their airlines before heading to the airport.

The head of one industry body said the organisation has “crucial questions to answer” over the fault, which Nats remedied three hours after confirming the issue just before midday on Monday.

Willie Walsh, head of the International Air Transport Association, called the failure “unacceptable” and said he felt for passengers who continue to suffer “huge inconvenience” and airline staff put under “considerable additional stress”.

He added that airlines would “bear significant sums in care and assistance charges, on top of the costs of disruption to crew and aircraft schedules. But it will cost Nats nothing.”

Passengers have recounted how they faced huge disruption because of the issue.

Sarah Skellern is one of thousands of passengers caught up in the aftermath, with many unable to return home to the UK or fly abroad for long-booked holidays.

Mrs Skellern, from near Preston, Lancashire, described “absolute chaos” at Palma de Mallorca Airport, after waiting on an aircraft for six hours before her Jet2 flight on Monday was cancelled.

After leaving the plane, Mrs Skellern said she and her husband Barry, and two boys Toby, 10, and Gabe, eight, were left to find their own accommodation. A lack of local hotels meant they had little choice for a bed but the Spanish airport floor. They eventually got a flight home on Tuesday.

Adam Ashall-Kelly and Christine Marriott fear they could miss their wedding in Italy, after their flight from Manchester to Verona was cancelled on Monday.

The bride and groom-to-be are frantically trying to find a way to get to a local court in Malcesine, near Lake Garda, before they can be legally wed on Saturday.

The couple, both from Manchester, have booked a new flight to Milan on Wednesday but have “no idea” whether it will go ahead or be cancelled.

Analysis of flight data websites showed at least 281 flights – including departures and arrivals – were cancelled on Tuesday at the UK’s six busiest airports.

This consisted of 75 at Gatwick, 74 at Heathrow, 63 at Manchester, 28 at Stansted, 23 at Luton and 18 at Edinburgh.

Airports and airlines were forced to apologise to travellers for the delays and cancellations, and in some cases have offered passengers full refunds.

Heathrow Airport – the world’s busiest two-runway airport – said on Tuesday there may be some continuing disruption on some routes and advised all passengers to check their airline before travelling to the airport.

EasyJet had been disrupted on Tuesday but by the evening said it was now operating normally.

Michael O’Leary, boss of Ryanair, said it had had to cancel about 250 flights on Monday, affecting about 40,000 passengers. On Tuesday 70 flights were cancelled, he said, adding that the airline was hoping to run a “normal operation” on Wednesday with “minimal delays”.

“It is sadly outside of our control,” Mr O’Leary said. “We have been in contact with UK Nats, we still haven’t had an explanation from them – what exactly caused this failure yesterday?”

BA has advised customers travelling on short-haul services to check their flight was still running before heading to the airport.

The airline added that customers due to travel on a short-haul service on Tuesday or Wednesday may be able to move their flights to a later date free of charge.

Tui said that on top of a refund its customers would be entitled to a “future holiday voucher of £100 per person”.

The CAA says an airline has a duty of care to provide food, drink and accommodation if delays stretch overnight.

If a flight is cancelled, passengers should be offered a choice of a refund or alternative travel arrangements at the earlier opportunity.

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