Willie Walsh, chief executive of BA owner International Airlines Group (IAG), said human error was behind the power surge which is thought to have knocked out computer systems and disrupted the travel plans of more than 75,000 passengers around the world.

Speaking in Mexico at the annual Iata annual meeting, Walsh said an engineer had disconnected a power supply and this had caused a surge when reconnected without following the correct procedure.

“It’s very clear to me that you can make a mistake in disconnecting the power," he said. "It’s difficult for me to understand how to make a mistake in reconnecting the power.”

While BA has not revealed details of its external contractor, Walsh stressed the engineer responsible was authorised to be in its main Heathrow data centre, but not to "do what he did".

IAG had appointed an external investigator to look into the whole episode, and Walsh said the carrier would be happy to share its findings in due course.

A number of IT experts have questioned BA’s claims, suggesting the airline should have systems in place to manage an unexpected power surge.

Reports in the national press have claimed data centre uses outdated equipment, and that the air conditioning is inadequate to cope with the heat it generates.

Meanwhile, BBC News reported Walsh admitted BA had handled the crisis badly.

“I wouldn’t suggest for one minute we got communications right at BA, we didn’t,” admitted Walsh.

BA is now handling claims for compensation under EU law, after initially directing customers to their travel insurers, travel agents and tour operators. It has drafted in extra staff and has promised to settle payments within 14 days.