British Airwayshas confirmed the cause of IT issues that brought huge disruption to its schedule on 27 May and subsequent days.

"There was a loss of power to the UK data centre," says the IAG-owned UK airline, noting that this "was compounded by the uncontrolled return of power which caused a power surge, taking out our IT systems".

From 12 to 30 June flights to EU countries from 763 UAH one way

BA asserts that the episode was "not an IT failure and had nothing to do with outsourcing of IT". Rather, it happened because the electrical power supply was "interrupted", says the Oneworld carrier.

"We are undertaking an exhaustive investigation to find out the exact circumstances and most importantly ensure that this can never happen again," it adds.

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IAGchief executive Willie Walsh had already ruled out hacking as the cause of the problems, telling UK newspaperThe Times: "We didn't lose any data. We didn't have any data corruption."

He also stressed the company's commitment to upkeep of its systems. "We invest billions in new equipment," he is quoted as saying. "If investment is required, we make the investment.”

For the BA brand, the problems were "clearly damaging", Walsh conceded, adding: "We have got some work to do... I wouldn't wish it on anyone."

But he defended BA chief Alex Cruz from criticism. "It was not something caused by Alex. He did as good a job as he could have done in the circumstances."

In an update posted to its website this morning, BA says it is now "running a normal operation" again.