That's irrelevant to the legal position that retailers cannot have differential prices charged to customers based on thbusiness's cost of receiving payments. Also as you will find in mant threads here, quiote a few members of the public are quite used to carrying cash and using it, and as with card payments, the business carries the cost of each method their customers use.
Payment for retail goods and services has been clearly defined for many years. Decades ago, when plastic cards were new, there were many attempts to differentiate between credit and debit card use in retail. Both cards usually placed a basic handling charge per transaction on the retailer, whereas credit card issuers added the equivalent of the first 4-6 weeks of interes that roughly equated to the 'free credit' period before the holder's statement payment deadline. Sometime in the '70s ISTR, the banks largely equalised this charge. A few years later the government forced the banks to create student and low earner bank accounts which were likely to be less profitable than regular types. The banks response was to return to differential charges for debit and credit acounts. A few years later the EC/EU legislated that all transaction costs should be boren by the businesses involved. Gratefully, this legislation is still in force in post-brexit UK.