Santander is to close 140 branches, putting 1,270 jobs at risk, the Spanish-owned bank said.
The lender said the closures are in response to how customers are choosing to carry out their banking.
Santander has consulted unions on the proposed changes and will seek to find alternative roles for the 1,270 staff members affected, wherever possible.
The bank expects to be able to redeploy around a third of that number.
Susan Allen, Santander’s head of retail and business banking, said: “The way our customers are choosing to bank with us has changed dramatically in recent years, with more and more customers using online and mobile channels.
“As a result, we have had to take some very difficult decisions over our less-visited branches, and those where we have other branches in close proximity.
“We will support customers of closing branches to find alternative ways to bank with us that best suit their individual needs. We are also working alongside our unions to support colleagues through these changes and to find alternative roles for those impacted wherever possible.”
The company also said on Wednesday that 100 Santander branches will be refurbished over the next two years through an investment of £55m.
The refurbishments are planned to include a range of changes with a focus on personal service, convenience and community engagement.