Actually, even what you mentioned would never be a case anyway. Any and all businesses have a perfect right not to sell products or to provide a service to anyone they choose not to. A good example is a pub landlord, they have the right not to serve someone or a group of people and don't even have to give a reason. As far as i'm aware, the only exception to that rule are crown appointed services like the post office and some utility services. Our local post office though is inside a Londis store and there is a clear sign outside that says if you are barred from the store then you are barred from using that particular post office as well. Plenty of people now have to use another post office.