Consumers are being warned to be aware of 'exorbitant' and 'hefty' charges when using their bank account abroad.
Research by Which? has found that details of fees incurred by people when using their account abroad are often hidden away on providers' websites or undisclosed on statements.
Researchers went to Calais in December 2011 and compared the amount charged by each bank for the same €5.95 debit card purchase and a €20 ATM withdrawal.
Results show wide discrepancies between the best and worst providers.
Norwich and Peterborough's (N&P) Gold Light current account came out on top, as account holders aren't charged any fees for overseas use. By comparison, Halifax charged 33% more than N&P for the supermarket purchase.
Even when compared to its high street rivals, Halifax's fees for overseas purchases were much higher - charging 29% more than both HSBC and Barclays.
Lloyds TSB charged 15% more than N&P for the ATM withdrawal.
Additional charges when using a debit card can quickly add up when people are abroad.
For example, ten transactions of £50 made with a Halifax debit card would cost the cardholder £28.75.
Providers are now facing calls to be clearer about the fees they charge so that consumers can easily compare whether they are getting a good deal.
"Banks are charging exorbitant fees for the most straightforward overseas transactions, pushing up the price of even the most basic purchases," said Which? executive director, Richard Lloyd.
"We want to see overseas bank charges made clear to consumers when they sign up for their current account or credit card.
"Consumers must be able to easily see whether they are getting a good deal or not."
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