A power cut in Spain left customers of internet bank Cahoot, which is owned by Spanish bank Santander, unable to access their accounts for over a day.
The bank warned that any transactions made since 0730 on Wednesday might not be displayed for 24 hours despite being processed.
The power cut also affected Abbey, which is also owned by Santander.
Although some delays to direct debits might have occurred, Cahoot said there was no danger to savers' deposits.
"Cahoot is part of the Santander Group, one of the world's most successful and well-capitalised banks with nearly 70 million customers, and remains a safe place for your money," said Cahoot managing director Matthew Timms.
Cahoot has 750,000 customers and their website access was affected for most of Wednesday and Thursday morning. The group's call centre was also affected.
Mr Timms apologised to customers. He said that payments that should have been made on Wednesday were being processed on Thursday.
Customers would be able to claim back any money lost through charges as a result of the delay.
Abbey's website was operating shortly after the power cut struck, and Bradford and Bingley savers, whose accounts are now run by Santander, were unaffected.
Cahoot said its website was working by 6.45pm on Thursday.
^ Back to top | BBC Sport Home | BBC Homepage | Contact us | Help | ©
~RS~q~RS~~RS~z~RS~50~RS~)