General Licence everyone has unless it's revoked for criminal behaviour, with Shops their legal requirement is to ensure you are over 18 and not a banned person, they don't have a set way as such they just tend to go to Photo ID as it's the easiest way to verify things and match it to you to keep them legally in the clear should you misuse the Rifle.

What I would say is just call the shop, explain to them what ID you have (not being mean but I'm guessing visually you look over 18) and if its a RFD delivery driver they can probably just work with it to get you cleared.