Current account providers are using a myriad of baffling charging structures that make it almost impossible to calculate and compare the cost of slipping into an unauthorised overdraft, research from Which? has found.
The consumer group made its findings after asking 18 volunteers, including a principal inspector of taxes and a retired headteacher to calculate from a mock statement what this cost would be by looking at banks' and building societies' charging structures on their websites.
The volunteers got just 10 out of 72 calculations correct between them, with the tax inspector getting just one of his four calculations right and the former headteacher getting them all wrong.
It also took people 10 minutes on average even to find the charges on current account providers' websites - and in some cases it took longer than half an hour.
The research found that variations in language used by providers to describe unauthorised overdraft charges caused further confusion for consumers.
The different terms for this were found to include "informal", "unplanned", "unarranged" and "unapproved".
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Which? wants the Government to force banks to release the data they have about how customers use their accounts, which could be used to develop comparison tools that would allow consumers to rank providers by cost based on their own personal needs.
Earlier this month, Barclays announced new measures to simplify overdraft fees which would save its customers an estimated £14 million collectively in 2014, including a "one per day" cap on its £8 paid and unpaid transaction fees.
Which executive director Richard Lloyd said: "Consumers are faced with a myriad of complicated charges for using an unauthorised overdraft, and it's virtually impossible for people to calculate and compare the cost of running a current account.
"It's no wonder so few people switch between banks when you can't easily compare prices."
Figures released by the Payments Council this week showed there had been a recent upswing in people swapping bank accounts following the launch of a new industry guarantee launched in September to help shake up competition and boost consumer confidence in switching.
The guarantee has cut the length of time it takes to switch accounts to seven working days and also means that incoming and outgoing payments are automatically swapped over to the new account.
The Payments Council said that more than 300,000 people switched their current account in the last three months of 2013 - marking an increase of almost one fifth (17%) on the same period a year earlier.
Eric Leenders, executive director of retail for the British Bankers' Association (BBA) said: "Banks already help customers to compare account charges in a variety of ways such as making literature available in branches and online calculators.
"They also itemise charges on bank statements and use text alerts to communicate important account information instantly.
"All the major banks also make information about customers' current account use available to them in a downloadable format as required by the government's midata initiative to encourage transparency.
"The good news is that across the board overdraft charges have plummeted since 2008, with estimated consumer savings of up to £928 million over the past five years."
A Government spokeswoman said: "The Government is clear that consumers must be able to easily access clear and transparent information about the charges that may apply for overdraft fees.
"Through the midata initiative the Government is encouraging banks to give consumers information about their spending patterns so they are able to find the best deal for them.
"They already have access to free text alerts when a balance falls below a certain level, a free seven day current account switching service, while a more robust regulatory system that will help deliver for consumers will be in place soon."
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