Problems with IT systems at the Royal Bank of Scotland stopped customers making online and card payments on the busiest shopping day of the year.
The cause of the problem that affected customers of RBS, NatWest and Ulster Bank has not yet been identified.
RBS said all services are now back working normally and offered to refund customers if they have lost money as a result.
“We would like to apologise to our customers. If anyone has been left out of pocket as a result of these systems problems, we will put this right,” said RBS in a statement.
“If any customer is experiencing issues this morning, they should get in touch with our callcentres or come into our branches, where our staff will be ready to help.”
The banks' IT systems have been hit several times over the last couple of years. In summer 2012, the banks' customers were unable to access their accounts for days, as a result of software issues.
The glitch in the CA7 batch process scheduler ended with 12 million customer accounts frozen. Customers were left unable to access funds for a week or more as RBS, NatWest and the Ulster Bank manually updated all the account balances. RBS said the problems cost the bank £175m.
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As a result of the software glitch, the Financial Services Authority (FSA) demanded details of how major banks planned to prevent a repeat. Then, in March 2013, the bank experienced further disruptions as ATM, online and telephone banking services were hit by IT problems
The problems meant customers had difficulties making cash withdrawals and debit card payments, as well as disruption to online and telephone banking.
Jean-Louis Bravard, director at Burnt-Oak Partners and former CIO at JP Morgan said: “After yesterday’s fiasco and the earlier problems in 2012, it is painfully apparent that the RBS Group has systemic IT problems.
“But it is most probably not alone in relying on obsolete legacy IT, surrounded by an ever-increasing plethora of newer systems to give consumers the impression that the banking systems are fit for purpose in our internet and smartphone world. They are not and the FCA and the bank boards are in denial.
"Bank IT in the UK is not OK.”