Santander is to close 111 branches across the UK – a fifth of its network – which it says is in response to the shift to digital banking, accelerated by the pandemic.

The bank also announced a shake-up of its office sites that will lead to four locations being closed and its UK headquarters being moved from London to Milton Keynes. About 5,000 staff are affected by the offices announcement, and Santander said they would be offered new arrangements combining working from home with “access to local spaces designed to enable team collaboration”.

Santander said the majority of branches to be closed were less than three miles from another Santander branch, and the furthest distance was five miles.

In addition, the bank said all current and business account holders would still be able to bank in person at more than 11,000 Post Office branches.

Santander said Covid had quickened changes in customer habits, with branch transactions falling by a third over the two years before the onset of the pandemic and by a further 50% last year.

The closure programme will start on 24 June, with four branches in London and one in Glasgow among the first to shut. All 111 are to be closed by the end of August.

Many of the big banks have been cutting their branch networks, claiming customers are spurning traditional counter service in favour of banking online and via mobile phones. Many have said the pandemic has sped up this process.

In January HSBC announced it would be closing another 82 branches this year, and this month Marks & Spencer’s banking arm, M&S Bank, said its 29 in-store branches would close in early July.

According to the consumer body Which?, banks and building societies have closed or announced the closure of 4,188 branches since January 2015, averaging around 50 each month.

“Branch usage by customers has fallen considerably over recent years so we have made the difficult decision to consolidate our presence in areas we have multiple branches relatively close together,” said Adam Bishop, a Santander executive.

He said Santander, which will continue to operate 452 branches across the UK, expected that the size of its network would now remain stable “for the foreseeable future”. He added: “We continue to believe that branches have an important role to play.”

However, Which? said this latest announcement meant Santander had closed, or earmarked for closure, 470 branches since 2015.

Gareth Shaw, its head of money, said: “The bank branch network continues to shrink at an alarming rate, often leaving entire communities without somewhere to withdraw cash or speak to someone face-to-face about sensitive financial matters.”

He added that while many consumers could benefit from digital banking, “shutting branches has a significant impact on those who still rely on them for essential banking services like withdrawing cash, particularly if they are vulnerable”.

Shaw said that banks looked set to continue to make such changes without having put in place suitable alternatives and despite the Financial Conduct Authority asking firms to reconsider branch closures during lockdown. “The government must urgently set out its plans for introducing legislation protecting access to cash.”

In total about 840 staff work in the branches due to close, and Santander said it would be working to find alternative roles for them wherever possible. More than 200 roles will be available in nearby branches, and there will be other internal opportunities for redeployment, it said.

Separately, Santander announced plans to consolidate its office sites into six main locations across the UK and introduce more flexible working. Milton Keynes, where the bank is investing £150m in a new campus, will become its UK headquarters, alongside bases in Belfast, Bradford, Glasgow, London and Sheffield.

As part of the changes, Santander will close its Bootle, Newcastle, London Portman House and Manchester Deansgate offices by the end of 2021. It will also reduce the amount of office space at its current headquarters at London’s Triton Square, near Regent’s Park, as well as at its London Ludgate Hill, Leicester Carlton Park and Teesside sites.