Thousands of Abbey current account customers are facing delays in receiving their salaries and benefits following a technical error at the bank.
The error meant payments that were due to be processed overnight have not been credited to people's accounts, while direct debits and standing orders that were supposed to leave them have also not been paid.
Abbey said it had now fixed the problem, and was "urgently" processing these payments.
Some people have already received their payments and Abbey promised other customers the money would be in their accounts by the end of today at the latest.
It added that any direct debits and standing orders would also be paid today and customers would not incur any charges as a result of the error.
It is not known exactly how many people have been affected by the problem.
Abbey, which is part of Spanish banking giant Santander, has around six million current account customers, although only people expecting a credit to be paid into their account or a payment to leave it will have been affected.
But a high proportion of people are likely to have been impacted as many workers receive their salaries early during December, ahead of the Christmas break.
An Abbey spokesman said: "Due to a technical error, payments that were due to be processed overnight have not been. We are urgently processing these payments.
"We apologise to any customers who were expecting a credit and can assure them this will be in their account today.
"Any direct debits and standing orders due to go out of a customer's account today will still be paid in the normal way today and no customers will incur any charges as a result of this error."