The fine relates to operational risk and governance failures connected to the bank’s IT upgrade programme in 2018.

The bank was fined £29.75m by the FCA and £18.9m by the PRA, including a 30% discount agreed with the regulators for settling promptly.

In April 2018 TSB updated its IT systems and migrated to a new IT platform but this was hit by technical failures resulting in significant disruption to the continuity of banking services, including branch, telephone, online and mobile banking.

A significant proportion of the bank’s 5.2m customers were affected by the issues, with some being affected until December 2018.

TSB has already paid £32.7m in redress to customers.

The FCA said the IT migration was an ambitious and complex programme with a high level of operational risk but the bank failed to organise and control it properly, including failing to manage the operational risks arising from its outsourcing arrangements with a critical third-party supplier.

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.”

TSB is a retail bank that provides banking services including current accounts, business banking, savings accounts, mortgages, insurance, loans and credit cards.