Banks were accused by Which? of using underhand methods to dissuade customers from seeking refunds, after they have been charged "unfairly" for exceeding their overdrafts.
Which? said that banks have threatened to close accounts, pass details on to debt collectors and charge for statements when customers challenge their overdraft fees.
Which? claims that it has heard of charges of up to £5 per page for duplicate statements. The law permits a maximum charge of £10.
One bank tried to charge £30 an hour labour charges to send duplicates, with a total bill of £360.
Doug Taylor, the personal finance campaigner at Which?, said:
"Banks are employing increasingly underhand methods to avoid their responsibility to treat their customers fairly and refund the charges."
Angela Knight, the chief executive designate of the British Bankers' Association, said:
"Which? is clearly trying to exploit its position as a consumer body by sensationalising what could be a useful piece of research.
The banking industry handles over seven billion transactions a year and occasionally something will go wrong that's human nature.
But the way in which Which? has approached this is also personally insulting to the front-line bank staff who do an excellent job serving their customers."
As I have said before, banks are on this earth to make money they are not a charity. Try to stop them making money in one way, and they will find another way to charge you.
Customers would be well advised to help themselves lessen the banks' avenues for charging, by keeping their bank statements for at leastr 6 years.