One day I was waiting for the bus, in a world of my own. Slowly a few other people added to the number, haphazardly positioned around the stop. 

When the bus arrived I moved in line with the doors. Noticing a few passengers inside the bus who were making their way to the front, presumably to alight, I took one step back. As I did so a person rushed in front of me to get onboard. I would normally not react to this sort of occurrence. On this occasion I declared, “you’re supposed to wait until people have got off!”
Months, and many trips have passed since this experience. This morning while reenacting the scene, I was reminded of it. This was immediately followed by questions: who made the rule? And, even though I prefer not to queue, was I outraged that someone jumped in front of me?
The answer to the former and the latter is, while I can’t remember being formally trained in the niceties of polite travel on public transport, it is an ingrained, British thing to give way to others.