TSB admitted late payments to customers overnight just a few days after a critical report on the bank's IT crisis last year.
The bank responded to a flood of social media complaints on Friday morning when it said, "Some TSB account payments have been delayed overnight and we are working to process them as soon as possible today.
"We apologize for the inconvenience caused and will ensure that customers do not stay out of their own pockets.
"If TSB customers need emergency money, please contact us at the number on the back of the card.
"Customers can still use their cards to make payments or withdraw money."
There was no information on what was behind the fault.
Customers reported not being paid and unable to pay bills as a result of the failure.
It came just days after the release of a report, revealed by Sky News, which showed several major failures in the run-up to last year's IT platform migration, leaving two million current account customers facing weeks of disruption.
Among the findings of the bank-prepared investigation was the failure to test a new data center.
TSB's final bill for the collapse is expected to exceed £ 400 million and would be even higher if regulators decide to impose a penalty.
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