Santander plans to close 140 of its branches in the UK, pointing to changes in how its customers are banking and an increase in digital transactions.
The closures will put 1,270 jobs at risk, with the bank expecting to relocate about a third of those affected.
Santander will retain a network of 614 branches after the changes and has committed to supporting its staff throughout the consultation process.
The Spanish-owned bank reported the number of transactions carried out at Santander branches had fallen 23 per cent over the past three years, with digital transactions growing by 99 per cent in the same period.
The bank is offering individual support to customers of closing branches to find alternative Santander branches and access digital, telephone and Post Office banking services.
Susan Allen, head of retail and business banking at Santander, said the way customers were choosing to bank had changed "dramatically" in recent years.
She said: "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."
Santander announced plans to invest £55m in the refurbishment of 100 of its branches over the next two years, including a focus on "personal service, convenience and community engagement".
Ms Allen said she was confident the proposed refurbishment would provide the "right branch network" for customers’ changing needs and expected the size of the network to remain stable for "the foreseeable future".
George McNamara, director of policy and influencing at charity Independent Age, said: "Once again, thousands of people around the UK are set to lose a local bank branch.
"With increasingly large distances between bank branches, this can cause difficulties for customers who rely on public transport.
"Banks must ensure that all customers can access services, advice and offers using their preferred method of communication, whether that be over the internet, on the phone or in person."