Customers of UK Internet bank cahoot were locked out of their accounts for over a day following a power cut in Spain, home of parent company Banco Santander.
The power cut knocked out cahoot's Web banking site at around 8am on Wednesday. The site was still experiencing difficulties on Thursday afternoon.
Cahoot's call centre was also hit by the power outage, leaving customers with no direct way to access their accounts.
Cahoot, which is a division of UK retail bank Abbey, has said that transactions made by customers after 7.30am on Wednesday might not be shown in accounts within the next 24 hours, but they will be processed today.
Abbey's Internet service was also hit by the power cut, but that site was back up far more quickly than the cahoot service. Bradford and Bingley customers were unaffected.