In the pub there is an invisible queue. I say so and so does Kate Fox in her book Watching the English.
Everybody waiting to be served in the apparently random cluster of people knows who was there first, and the staff behind the bar know it too. Any person who tries to jump the queue by smiling, gesturing or otherwise trying to attract the bar person's attention will recieve nothing except a polite smile in reply. A polite smile means wait your turn, you impatient so and so. Thus is pub harmony acheived.
A similar system operates in the travel centre at Oxford train station. That jumble of people in chairs is really a queue and everyone in it knows it, everyone joining it recognises it and anyone attempting to jump it will be politely smiled at.
The moral of the tale is this: no one ever said queues have to be a straight line. No one ever said anything.