New figures suggest more than 3 million British adults do not have a bank account.
The number is double previous estimates by HM Treasury's Financial Inclusion Taskforce, and four times what it was before the financial crisis of 2008.
Ffrees Family Finance reckons that 3,034,000 British adults are currently living without a bank account.
These households are excluded from financial services – such as direct debits – which could help them manage their money and save up for the future.
London, with 440,000 unbanked adults, accounts for 16 per cent of all those without a bank account – more than the entire population of Liverpool.
But the problem is countrywide. In Doncaster, for instance, there are 39,800 people without accounts, double the capacity of the home ground of local Championship football club Doncaster Rovers.
Areas with high numbers of unbanked adults also include Durham with 36,900, Coventry with 28,100 and Manchester with 17,100.
Alex Letts, chief executive at Ffrees said: "The data suggests a flight from the traditional banks since 2008 among the mid to lower paid.
"Perhaps that's because retail banks' current accounts are not really suitable for the majority of the population who want something more modern, and lower cost."
He suggested the figures also reflect the breakdown in trust between consumers and the banks after the financial crisis and the well-publicised mis-selling scandals.
"Either way, it reinforces the point that the time is ripe for a new model that works for families on average wages," Mr Letts said.Reuse content