Consumers are being charged up to £900 for going overdrawn, according to the Which? consumer group, highlighting the range of costs involved in 'free' banking.
Charges for going overdrawn for two days per month without permission ranged from £120-£900 a year.
Those who stayed in credit were still hit with charges for withdrawing and spending cash abroad and through lost interest.
Over half of the 2,000 consumers surveyed by the consumer group said they felt they had paid an unfair or hidden bank charge and 94 per cent felt banks should be more transparent with their charging.
The group wants to see all banks providing information on how much they charge for their accounts, portable account numbers to make it easier to switch banks and greater competition on the high street.

It also urged new regulator the Financial Conduct Authority to clamp down on high and complex overdraft charges.
Peter Vicary-Smith, Which? chief executive, said: "When some people are paying up to £900 a year in bank charges it completely shatters the myth that banking is free.
"The suggestion that banks should increase charges to avoid more scandals defies logic and is a slap in the face for consumers who are being hit hard by one of the worst financial crises in recent times.
"It's a disgrace that the very people who bailed out the banks are being asked to pay more for the most basic accounts, while the industry continues to be rocked by scandals like PPI mis-selling, LIBOR rate-rigging and IT failures.
"Banks must be far more transparent about their fees and charges so that people can clearly see what they already pay."