Barclays has pledged not to close branches in remote areas or where it is the last bank in town for the next two years.
The bank is also launching a new cashback scheme enabling people to withdraw money at small businesses - but said that from 2020 its customers will no longer have a facility which allows them to withdraw cash over the counter at Post Offices.
The bank's new cashback scheme should make it easier for customers to withdraw money at businesses in remote towns and areas without a branch or ATM.
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Barclays said the freeze on remote and 'last bank in town' closures will see more than 100 branches ring-fenced so that they remain until at least October 2021.
It is also exploring ways to boost demand in branches generally, starting initially with pilots in 12 areas.
Barclays said it remains "committed to the Post Office framework" and customers and businesses will still be able to pay in cash, cheques and check their balance - but the facility for over-the-counter cash withdrawals will end from January 2020.
Cash withdrawal by cheque will still be available, subject to arrangement.
It is writing to affected customers about the changes.
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Adam Rowse, managing director of branch-based banking at Barclay, said: "By maintaining last-in-town or remote branches over the next two years, and working with the community, we hope to increase demand and keep these branches viable.
"We also recognise that there are opportunities to support customers with access to cash where there is no branch or ATM nearby.
"We are launching a cashback offering working with merchants to give customers access to cash over the counter."
Barclays' new cashback scheme will enable customers to withdraw cash at businesses in remote towns and areas where there is no branch or ATM alternative within 1km.
It will launch in more than 200 locations from January 2020.
Meanwhile, Barclays is trialling how it can work with customers and communities, including MPs, councillors and business groups, to see if customer demand can be increased, which would help to make branches more viable in the longer term.
The 12 trial locations include Pickering and Yarm in Yorkshire, Wombourne in Staffordshire and Risca in South Wales.
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Part of the trial includes flexible branch opening hours and making technology available to extend services such as video banking.
Mr Rowse told the PA news agency: "We really want to focus on engaging customers in the local community.
"New technology allows even the smallest branch to become a full-service branch.
"We use video technology so our specialists across the country can help people with buying a home or starting a business or borrowing through a business or needing help or advice. That's what we're looking to do."
He said successes in the 12 trial areas could be quickly rolled out to other branches.
Mr Rowse continued: "We believe in the future that branches will be a lot more about education - about helping people with those things that are the most important in their life - whether it's: 'I'm opening my first account' or: 'I'm going off to university'... or: 'I'm starting a business'...
"We're really working with the local community to find out what it is that they want."
Barclays said "pop-up" banking facilities to help communities will also appear at 300 locations by the end of 2021.
Bank branch and ATM closures generally have sparked fears about people's ability to continue to access cash.
The Post Office, which has around 11,500 branches, offers banking services on behalf of many banks, but some commentators in the access-to-cash debate have argued that this should not be seen as a direct replacement for banks' own branches.
Some other banks and building societies have also recently announced initiatives to boost access to cash or keep branches open.
In March, Nationwide Building Society pledged that every town and city with a branch will still have one in May 2021.
In February, Lloyds Banking Group, in partnership with Visa, announced a pilot scheme to boost the number of retailers offering cashback.
Here are the 12 pilot areas where Barclays is looking at how customer demand in branches could be increased:
Yarm, Pickering and Guiseley in Yorkshire, Barnard Castle in County Durham, Wombourne and Kidsgrove in Staffordshire, Risca and Tredegar in South Wales, Shenfield and Burnham-on-Crouch in Essex, Esher in Surrey and Biggin Hill in London.
The 100 branches saved by Barclays
Last in town branches:
Alderley Edge
Bargoed
Barnard Castle
Barnoldswick
Biggin Hill
Bilbrook
Builth Wells
Burnham-on-Crouch
Cadishead
Carnforth
Chalfont St Peter
Cockermouth
Cuffley
Drayton, Norwich
Dunmow
Esher
Flitwick
Guiseley
Haxby
Hemsworth
Heywood
Histon
Holmes Chapel
Hoyland, Nether
Kidsgrove
Knowle
Llandeilo
Pickering
Radlett
Risca
Saltburn-by-the-Sea
Shenfield
South Woodham Ferrers
Southwick
St Ives
Tredegar
Treorchy
Wadebridge
Watton
West Mersea
Whickham
Woburn Sands
Wombourne
Wroxham
Yarm
Ystrad Mynach
Manningtree
Llangollen
Bentham
Keswick
Harleston
Southwold
Bedale
Leyburn
Framlingham
Oundle
Kirkby Stephen
Seahouses
Leiston
Haltwhistle
Stanhope
Middleton-in-Teesdale
Remote branches:
Bideford
Brecon
Brigg
Caernarfon
Camborne
Chipping Norton
Cranleigh
Daventry
Deal
Devizes
Driffield
Easingwold
Falmouth
Gainsborough
Heathfield
Helmsley
Helston
Horncastle
Kirkby Lonsdale
Lampeter
Launceston
Leek
Malton
Market Drayton
Mildenhall
Monmouth
Pocklington
Porthmadog
Prudhoe
Pwllheli
Richmond, North Yorkshire
Settle
Shaftesbury
Sheerness
Sleaford
Stow-on-the-Wold
Tenby
Thirsk
Towcester
Ulverston
Welshpool
Whitby
Workington