Why do you think we use "Mind the queue"? I've never heard that in my life.
An old friend was in London. She was at a bus stop with some other people and didn't know that the other people were formed in line. In the U.S., we don't form lines at bus stops, so she thought they were all just standing there waiting, as she was. When the bus door opened, she started to get on. Several people yelled, "Mind the queue, mind the queue!"
She had never heard the expression. We say line, not queue. Americans would say something like, "Wait your turn!" or "Get in line!" At first she didn't realize they were talking to her. She finally figured out was was going on and went to the end of the line - uh - queue.
So...maybe they just say it at one bus stop in London!