As a general rule it's best to ask beforehand with privately owned places (such as stores and shopping malls). Security have every right to keep you out of those places (as they'd do if you were wearing a crash helmet etc.) - and yes, a group of us got told to stay out of Tesco as we were wondering about on Halloween, though we were welcomed at Domino's, and invited into a live music night without having to pay! You're more likely to get a yes if you can provide a reason for wanting to do it - such as collecting for a charity (but if you are collecting you need to be registered to do that).
