It is “staggering” that the UK’s air traffic control system was caused to “collapse” by a piece of incorrect data, according to former British Airways boss Willie Walsh.

National Air Traffic Services (Nats) chief executive Martin Rolfe said the widespread disruption which started on Monday “relates to some of the flight data we received”.

Mr Walsh, director-general of global airline body the International Air Transport Association (Iata), told BBC Radio 4’s Today programme: “I find it staggering, I really do.

“This system should be designed to reject data that’s incorrect, not to collapse the system.

“If that is true, it demonstrates a considerable weakness that must have been there for some time and I’m amazed if that is the cause of this.

“Clearly we’ll wait for the full evaluation of the problem but that explanation doesn’t stand up from what I know of the system.”

Mr Rolfe was asked on the programme why the problematic flight data was not rejected by Nats “like a piece of spam”.

He replied: “Our systems are safety-critical systems, they are dealing with the lives of passengers and the travelling public.

“So even things like just throwing data away needs to be very carefully considered.

“If you throw away a critical piece of data you may end up in the next 30 seconds, a minute or an hour with something that then is not right on the screens in front of the controller.

“So it is nothing like throwing away spam.”

Former air traffic controller Michele Robson told the Sky News Daily podcast: “It’s a very old system, it’s been running for many years and generally we’ve been very lucky and we don’t often have failures, or if we do, we get it back during that back-up time, which is what it’s there for.

“There have been other instances in the past where something has been incorrectly formatted and the flight plan computer behaves in a way they’re not expecting and effectively causes it to fail.”

Asked about the inputting of flight plans, she said: “You have to space things in a certain way using a certain number of dots, as an example.”

She added: “It has to be something pretty unusual that they’ve input for it to happen, but it’s an old system that perhaps something was input (on Monday) that it’s never seen before and that’s what caused it to have this reaction where it’s failed.”