Ref the ice cream van ...
I understood that trading on the Prom was a strict No-No. If you have an event or display there, such as the ones I'm involved with, you have to apply for a permit to be allowed to collect for charity - event programme money goes to charity, you cannot actually sell them.
Perhaps our problem is doing things correctly. If you have cheek and take your chance you can get away with it! No-one around to ask questions.