Tens of thousands of holidaymakers were hit by the meltdown last Monday (28 August), the knock-on effects of which are continuing to impact some people’s return from the bank holiday getaway more than a week later.

In its report to the CAA, Nats said it had traced the issue to a flight plan processing sub-system, whereby one single flight plan – which included two identically named but separate waypoint markers outside UK airspace – caused the glitch, described by Nats as an "extremely rare set of circumstances".

A fuming Michael O’Leary, though, described Nats’ preliminary report as "factually inaccurate whitewash" that understated the impact of the outage, with the Ryanair boss urging Nats to come forward to explain why its back-up systems failed, and to compensate airlines for their service to customers.

"The least Nats could and should do is to reimburse its airline customers for the tens of millions of pounds they have spent reimbursing passengers for their hotel, meals and transport expenses, which were entirely due to Nats system failure," said O’Leary.

He added: "If Nats fails to reimburse its customers for these expenses, then [transport secretary] Mark Harper should intervene as the largest shareholder in Nats and instruct Nats to reimburse Nats airline customers for these right-to-care expenses."

The CAA has confirmed it will conduct its own independent review of the incident and Nats’ response, threatening "appropriate action" should the air traffic control operator be found to have breached its statutory and licensing obligations.

Lo Bue-Said said she was concerned on behalf of the UK’s wider outbound travel sector that the efforts to investigate the outage would not go far enough, and would fail to recognise the impact on agents and tour operators caught up in the maelstrom.

"As part of its review, we would urge the UK CAA to review the impact of the Nats technical failure on the entire travel industry eco-system," said Lo Bue-Said. "Travel agents [and] tour operators [were] all hugely impacted by the disruption too, working around the clock for their customers."

Lo Bue-Said added: "The entire travel industry supply chain was impacted. This, could also form part of the review with travel agents and tour operators hugely impacted too, playing a key role in the mopping up process – bringing Brits home, communicating and hand-holding during times of uncertainty."

Airlines can’t be left to carry the can

Airlines UK, meanwhile, said that while it welcomed the CAA’s independent review, it was concerning such a small fault led to such dramatic consequences for passengers and airlines, with chief executive Tim Alderslade also critical of the length of time it took to rectify the situation. "Lessons must be learnt," he said.

Alderslade also echoed O’Leary’s concerns. "Airlines worked round the clock in response to the situation, providing accommodation to passengers and putting on more flights to bring them home as quickly as possible, at huge cost to all carriers impacted," he said.

"Airlines cannot be the insurer of last resort though and there must be accountability from Nats when things go wrong. Airlines are seeking clarity on what options exist for Nats to cover our costs under the current legislation and will continue to engage with government on all options for redress.

"We can’t have a situation whereby airlines carry the can every time we see disruption of this magnitude."