More people and businesses will be able to do their everyday banking at the Post Office under a new agreement.
The Post Office said new, simplified arrangements with the banking industry mean 99% of UK personal banking customers can do their day-to-day banking at the Post Office, up from 95% previously.
The proportion of business customers able to do their day-to-day banking at the Post Office has nearly doubled, from around 40% previously to over 75%.
The new agreement has standardised the banking services that customers are able to receive at the Post Office.
Previously, the arrangements had differed, depending on which bank a customer was with.
The move is part of efforts to minimise the impact of banks shutting their branches on communities, as more people move to online and mobile banking.
Nick Kennett, chief executive of Post Office Financial Services, said: "Access to cash plays a vital role in many local communities, acting as the lifeblood to consumers and small businesses."
In December, research from Which? found that more than 1,000 high street bank branches have closed over the past two years.
According to Which?, HSBC's branch cuts had equated to about a quarter of its network, while the RBS and Lloyds banking groups had made branch cuts equating to around 10% and 14% of their networks respectively.
The British Bankers' Association (BBA) said in December that the digital revolution in the way people manage their money has had an "inevitable impact on the use of bank branches, which has led to a number of branch closures".
The BBA said the decision to close a bank branch "is never taken lightly".
The Which? research also found that while many people rated the Post Office's services as good or excellent, there was a lack of awareness that it offered banking services.
The Post Office said the partnership will see it work more closely with banks and the Government to raise awareness of the services available to customers who require face-to-face branch services.
The simplified service, described as the biggest expansion of face-to-face banking in a generation, offers cash withdrawals, cash and cheque deposits and balance inquiries.
The Post Office, which has 11,600 branches across the UK, said customers will also benefit from longer opening hours as part of a modernisation programme, with over 4,000 branches being open on Sundays.
Some 99.7% of the population live within three miles of a Post Office branch, and in 2015 over 100 million banking transactions were carried out at its branches under arrangements with partner banks.
Business minister Margot James said: "Millions of consumers and small businesses across the UK will now benefit from unrivalled access to banking services, including on Sundays, thanks to the Post Office.
"This is the biggest expansion in branch banking services in a generation and I am delighted the network is able to offer these services to so many customers."
Economic Secretary to the Treasury Simon Kirby said: "I welcome these ongoing efforts to open up banking services so they're more convenient for everyone that uses them."