Santander UK says it is to cut 111 branches amid a customer drive towards online banking but it expects to retain a "significant" number of the staff affected.
The lender said its decision – aided by COVID-19 disruption – would be implemented by the end of August and leave it with 452 high street sites.
It added that most of those to be closed down would be within three miles of another branch.
The decision follows a widespread industry trend over many years that has seen banks move to cut costs by pulling out of town centres and invest in their digital offerings instead, to the fury of many customers.
The company charted a 33% fall in branch transactions in the two years before the virus crisis.
It reported a further decline of 50% during the pandemic-ravaged year of 2020.
Santander said 840 jobs had been placed at risk under the branch shake-up and there were opportunities for at least 200 of those people.
Its plans also included a major cutback in its office space requirements, which it said was based on staff feedback related to working from home during the pandemic.
It said that while 5,000 staff would be affected by those changes, no-one would lose their jobs.
The company explained that its office space would be consolidated into six main locations, with its Milton Keynes premises being designated its headquarters.
As a result, the Bootle, Newcastle, London Portman House and Manchester Deansgate offices were to be shut by the end of 2021, Santander said, under an agreement with unions.
It released the news just hours after rival lender Nationwide revealed a "work anywhere" strategy – the latest major industry player to reveal cutbacks in office premises.
Adam Bishop, head of branches at Santander, said: "Branch usage by customers has fallen considerably over recent years so we have made the difficult decision to consolidate our presence in areas where we have multiple branches relatively close together.
"We will provide every support to 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."