I think that ems (post #4) is probably right about Britain. However, as I haven't worked there for fourteen years, I can't be sure about how things are today.
I think it really depends on your work environment. If everyone is very relaxed, casual and friendly, then they might all refer to each other by contracted names, nicknames etc, regardless of their grade. I think the more serious the work environment, the less chance there is of such informality.