Having a walk few weeks ago and doing some Christmas-shopping I realised that depending if you pay with Euro or Pound you could get a really expensive price instead a fair price. It's known that you are always going to pay an "extra" when you are abroad, maybe because there are some hidden costs or a hidden fee because you are using a different debit card, however in the next pics I consider that you are paying an overestimate price.
Real currency value when pictures were taken
1 GBP = 1.15681 EUR 1 EUR = 0.864450 GBP
If the price is 38.00 GBP you should pay 43.9826 EUR instead 58 (difference over 14 EUR)
If you are travelling abroad, be sure you are getting the cheapest exchange rate or in the worst case scenario you should use your debit card, surely you will get a bad exchange rate but at least you won't pay an extra fee getting cash..and always, if you can, try to pay in the local currency.