TSB will close 164 of its branches and cut nearly 1,000 jobs, blaming “a significant shift in customer behaviour” as more customers bank online.
The figure is in addition to the 82 branches it said it would close in November, when it set out plans to save £100m by 2022.
Union Unite described the move as “a dark day for the finance sector”.
TSB boss Debbie Crosbie said the closure plan was not an easy decision.
From the end of next year the bank will have 290 branches – down from 540 currently.
The bank hopes most of the job cuts will come through voluntary redundancies, and said it would also create 120 new positions.
It did not name which branches would shut, but said those with the lowest footfall would go.
“Our customers are banking differently – with a marked shift to digital banking,” said Ms Crosbie.
“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.”
Unite’s national officer Dominic Hook said: “Unite has argued for some time that the financial services industry has a social responsibility not to walk away from its local customers who continue to need access to banking in bank branches.
“It beggars belief that just seven years ago TSB had 631 local branches and this announcement will reduce that number to merely 290 branches. “