Okay so it's complicated - "wait a minute" in the UK does not mean wait for one minute; it means wait for a short time. If you want somebody to wait for one minute exactly, you should say something like "wait a minute, literally one minute." But as with anything in English, context is everything. For example "wait a minute" can also be used in the sense of "just give me a chance to think about that." This needs to be illustrated further
Andy: You still owe me ten dollars. You never paid me back.
Phil: Wait a minute, I bought you that drink yesterday, doesn't that mean anything?
Andy: Oh yeah, sure