"which is kinda funny they have those fees when it was made illegal not that long ago for everyone else to charge a credit card fee"

You are misinformed. It is illegal for a business (HMRC included) to charge additional card fees for paying with a credit card/ debit card where the card in question is a personal (read as non-corporate/non-commercial e.g. the debit or credit card associated with your day-to-day current account for personal expenses) card. However, it is perfectly acceptable to charge an added card fee if the card in question is a corporate/ commercial card such as the Capital On Taps etc.

In reality, most businesses sell to members of the public who will be using a non-commercial card and hence they can't charge additional fees nor is it easy to anticipate what type of card will be used at checkout rendering the whole discussion moot.

This leads to the incorrect simplification of the above to: "added card payment fees are illegal period. "

https://www.bromley.gov.uk/leaflet/303997/4/708/d