TSB is to shut 82 branches as part of a £100m cost-cutting drive, the bank has announced.
The closures, which make up about 15% of the overall number, is part of a three-year turnaround plan by the high street lender.
Up to 400 jobs could be at risk from the cutbacks, although TSB has said it will try to find new roles for those staff affected elsewhere in the group.
A full list of the sites earmarked for closure is due to be published on Thursday.
The move comes as the bank attempts to turn around its fortunes after last year’s IT fiasco, which left nearly two million people locked out of their accounts and led to the then chief executive Paul Pester to step down.
TSB said it was aiming for a profit after tax of up to £140m by 2022, from a current break-even position.
The cost of the shake-up has been put at £180m.
TSB boss Debbie Crosbie said: “The plan we’re sharing today involves some difficult decisions, but it sets TSB up to succeed in the future.
“Taken together, these changes will help us to serve more customers, better, for the long-term.”
The overhaul will see the bank follow in the footsteps of its larger rivals like Lloyds and RBS by reducing branches and putting money into its online and mobile services.
The bank said it expects up to 80% of its sales to be digital by 2022, compared to 46% in September this year.
TSB also said it had around twice the number of stores per 10,000 customers in 2018 as the average in the UK.
“With a trusted brand, modern platform, and national presence, TSB is well placed to deliver – but we need to make changes to enable us to compete,” Ms Crosbie said.
“Our new strategy positions TSB to succeed in a challenging external environment at a time when we know customers want something different and better from their bank.”
It comes after a damning report last week that criticised TSB’s board for lacking “common sense” in the lead-up to last year’s IT debacle, when a computer upgrade went spectacularly wrong in April last year.
An independent investigation by law firm Slaughter and May found the lender’s board should have done more to challenge bosses in charge of the project.
The technology meltdown led to one of the UK’s biggest ever banking systems crises and as well as freezing people out of their accounts triggered an unprecedented wave of opportunistic fraud attacks on customers.
Just five months later it was forced to apologise again after many customers were once more left unable to access their accounts.
And only in the last few days, a fresh glitch meant some customers were left without wages in their accounts after the lender failed to process a number of overnight payments.