TSB is set to close 164 branches and reduce its headcount by around 900 people as it follows its customers, who are increasingly banking online.
The bank said it expects most of the 900 redundancies to be voluntary but did not rule out forcing staff out.
TSB said its branch network would be the seventh biggest in the UK after the closures reduce it by a third and added that more than nine in ten customers will have less than 20 minutes travel to a branch.
TSB chief executive Debbie Crosbie said: “Closing any of our branches is never an easy decision but our customers are banking differently – with a marked shift to digital banking.
“We are reshaping our business to transform the customer experience and set us up for the future. This means having the right balance between branches on the high street and our digital platforms, enabling us to offer the very best experience for our personal and business customers across the UK.
“We remain committed to our branch network and will retain one of the largest in the UK.”