From a total of 20,583 branches in 1988, only 7,586 remain, the consumer group Which? calculated.
Researchers said that while this was not a complete like-for-like comparison, it gave a good indication of the shrinking size of the network.
In Yorkshire, around one person in four does not live within two miles of a bank branch, and nationally, nearly one in 10 has to travel more than three miles, it said.
Which? also said that a survey of more than 2,000 people found nearly half unaware that they could access their high street current accounts at the Post Office.
The organisation said the scale of bank closures was “staggering”.
Its money editor, Ceri Stanaway, said: “It has left millions of people struggling to access the vital financial services and cash that they need.
“For many there is simply no substitute for a dedicated branch and the wide range of services it offers and many customers now face having to travel long distances if they are to avoid financial exclusion.”
The organisation said banks should be made to “properly justify” their reasons for closing a branch and take into account their customers’ needs.
It pointed out that not all banking services are currently available at the Post Office and that banks often demand that customers call into a branch for anti-fraud checks, or to discuss important legal documents.
Which? also said that with many communities facing the withdrawal on not only their bank branch but also their cash machine, action was needed to make sure people were not “financially excluded” and denied access to cash.
Gillian Guy, chief executive of Citizens Advice, said: “We also found relatively few people know that post offices provide basic banking services.
“Of those who did know, only about one in two said they were using them.
“We want the Government, the Post Office and banks to raise awareness and help improve the banking services post offices offer, to ensure they meet consumer needs.”