Following new EU regulations, capping debit card interchange rates (the price charged by the card owners e.g. Visa & Mastercard, to your merchant account supplier), some companies may see an increase in their card costs, initially with Visa.
Visa’s change is going to make it cheaper for the card processors to process low-value transactions (under £35) but (possibly a lot) more expensive to process transactions over £35. Currently, card processors pay a flat 8p to process a standard UK Visa debit chip and pin payment. From 1st March 2015, that flat fee was replaced by a fee of 0.2% of the transaction value plus 1p, but capped at 50p. NOTE: this is not what you are charged, as your provider will add costs and profit to the figure.
You should soon be receiving your first statement after the Visa increases on March 1st, so ensure you start making comparisons and be prepared to change your provider!