From what I have seen of the people that do this up in London they don't have any special permision (I may be wrong)
Gym Box regularly send out people dressed as giant boxers to advertise and hand our leaflets and one guy on Durastilts (he wanted to get some PJ's so we chatted for a while
Best people to ask are the local police as they will be the ones moving you on and should know about any licenses you would need
The main thing it to be safe as then most police /councils will leave you alone to ply your trade
The only time I have heard that you need permision and licenses is collecting money for charity but as you are advertising that shouldn't apply to you
Private shopping centers are a different kettle of fish
you need to seek permision from the management team but if the shop is in the center they should be able to sort that for you
I believe Kiola did some of this sort of work (he mentioned a shopping center to me ages ago) but he isn't on here very often so a PM might get a reply from him
Lastly good luck with it sounds like a fun way to earn a living
Jason