TSB has been fined nearly £48million over an IT meltdown in 2018 that left customers unable to access their online bank accounts for weeks.
The issue occurred after the high street lender moved customer data to a new computer system.
This transfer, however, saw TSB servers experience severe faults including branch, telephone and online banking.
After a five-year-long investigation into the incident, the Financial Conduct Authority (FCA) and the Prudential Regulation Authority (PRA) said the failings were "widespread and serious".
They further claim the incident led to "significant disruption" for many of TSB’s five million customers.
The watchdog reported that some of TSB's customers experienced ongoing issues for several months until the bank managed to return to business as usual.
The regulators said that while the data moved over to the new system successfully at the time of the upgrade, the new platform immediately experience technical failures.
The regulators' also found that TSB had failed to organise and control the IT migration programme adequately, and it failed to manage the operational risks.
The PRA said the disruption caused by those failings “fellow below the standards” expected of UK banks.
Overall, TSB was fined a total of £47.86million which is made up of a £29.75million penalty from the FCA and a fine of £18.9m from the PRA.
The fine adds to the £32.7million already paid out by TSB to retail and corporate customers impacted by the debacle.
TSB would have been slapped with a £69.5million fine but received a 30% discount as it agreed to resolve the matter.
This is yet another financial blow to TSB.
In 2018, the bank said the incident has cost them £330million as well as 80,000 customers who switched away from the bank.
Mark Steward, executive director of enforcement and market oversight at the FCA said: "The failings, in this case, were widespread and serious which had a real impact on the day-to-day lives of a significant proportion of TSB's customers, including those who were vulnerable.
"The firm failed to plan for the IT migration properly, the governance of the project was insufficiently robust and the firm failed to take reasonable care to organise and control its affairs responsibly and effectively, with adequate risk management systems."
Commenting on the fine today, TSB chief executive Robin Bulloch said: “We’d like to apologise again to TSB customers who were impacted by issues following the technology migration in 2018.
“We worked hard to put things right for customers then and have since transformed our business.
“Over the past four years, we have harnessed our technology to deliver new products and better services for TSB customers.”
