HFC Bank, a consumer lending business owned by HSBC, has admitted violating data protection laws when it revealed personal customer details in an e-mail, according to a report by the BBC.
According to the report, HFC sent urgent e-mails to 2600 customers, but an error meant that each address was visible to every customer on the list. The problem was made worse when customers' out of office messages began to respond, many containing telephone numbers.
The bank's corporate director Martin Rutland has apologised for the error, but the BBC says many customers are still unhappy and are considering taking legal action.
The bank has since credited affected customer accounts with £50 in compensation.
HFC says a member of staff made the mistake last Tuesday, when three e-mails were sent to groups of more than 800 customers asking them to call a helpline number.
The Information Commissioner told the BBC that HFC has broken the law, but it would not be taking action against the bank on this occasion.