British Airways might have to pay £100m in compensation, customer care and lost business due a major IT system failure that affected more than 1, 000 flights over the weekend from Hearthrow and Gatwick.

Although the services resumed on 28 May but as many as 200 BA flights in and out of Hearthrow were cancelled on Sunday, according to a Guardian report.

British Airways has said that the IT failure is believed to be caused by a power supply issue. The airlines also said that there is no evidence of a cyberattack.

James Walker, chief executive of Resolver, a free flights compensation claim site, said BA handled about 120,000 passengers a day in and out of Hearthrow and Gatwick, hinting a bill close to £50m for delays of more than three hours, suggests the report by Guardian.

Half of those passengers were likely to be entitled to meals and accommodation and a number of passengers will have asked refund or decided to avoid using BA.

Walker said BA would have to pay out compensation under the EU scheme that requires payment for flights delayed by three hours.

"This is not like an ash cloud or traffic controllers' strike that can't be predicted. The computer system breaking down is within its control. BA is going to have to pay out and it looks like its costs will be north of £100m," Walker told Guardian.

Last year the US airline Delta lost $100m (£78m) following power shutdown in its data centre that led to delays.

John Strickland, director of transport consultancy JLS Consulting, said BA was likely to face a "significant financial impact" as its problems expected to continue into this week.

Alex Cruz, chief executive officer of BA, in a YouTube video said all the IT systems were not yet restored.

"Many of our IT systems are back up today. All my British Airways colleagues on the ground and in the air are pulling out all the stops to get our operation back up to normal as quickly as we possibly can, we're not there yet," said Cruz.

"I know this has been a horrible time for customers. Some have missed holidays, some have been stranded on aircraft, some separated from bags and some stuck in long queues while they have waited for information. On behalf of everyone at BA I want to apologise for the fact you've had to go through these very trying experiences," added Cruz.