During their August holiday in France, Mr Brown paid between 1.5 and 2 per cent more for his francs when he used his Barclaycard, than his wife did with her Clydesdale Bank Access card. Using the Barclaycard added at least pounds 6 to the couple's holiday bill.
The discovery came too late for them to do anything about it this time - they found out about the different charges only when they compared bills earlier this month.
Mr Brown, a company director from Richmond, Surrey, said: 'Our holiday was very pleasent, but it has left us with that nasty little sting in the tail.
'When we received our respective statements, I found that my exchange rate for a purchase credited on 4 August was Fr8.07 to the pound.
'Barbara's statement for a transaction that went through on the same day worked out at Fr8.17 to the pound. On 17 August, my Visa rate was Fr7.97 to the pound, while my wife's Access rate was Fr8.10.'
A Barclaycard spokeswoman said: 'There can be three reasons why there may be discrepancies in exchange rates. The first is that even if a purchase took place on the same day the rate depends on when the retailer presents the invoice. Rates may change in- between times.
'There is also the fact that Visa and Access fix their rates in slightly different ways, fixing their prices at different times of the day. Finally, Barclaycard adds 2.65 per cent on top of the Visa rate as its own charge on each transaction.'
A Clydesdale Bank spokesman agreed with the first two reasons for a possible difference in rates between his bank's card and Barclaycard.
He added: 'The most interesting thing is that we only charge 1.6 per cent on top of the actual exchange rate. That is what makes the biggest difference to the prices paid on our card and the other one.'
Mr Brown said: 'In this instance, the amount we spent was small. But for a family spending long periods abroad or a business person making regular trips, the difference could be quite large.
'The lesson seems to be that if you have a choice between cards when travelling, always check the cost first and choose the cheapest.'
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