I have been reading “How to Stay Sane” by Philippa Perry and came across the gem that is Negative-Positivity, and by george does it explain a lot about London.
Essentially (please excuse my paraphrasing) politeness changes depending on if you are in a overpopulated area or not. In places like America where there is a lot of open space, the polite thing to do is to go up to people and make their acquaintance. You can be loud and personable because there is space. In that type of country (I say country because this type of behaviour has been ingrained through the generations) it would be considered impolite to ignore someone.
However in a crowded place like London, negative-politeness comes into effect. When there are so many people about, the polite thing to do is give them as much space as possible – be that physical or by just avoiding eye contact. While London is famed for people being ignored on the underground, actually we are just being as considerate as possible under the circumstances. If my face is in your armpit, the only thing this negative-politeness will let us do is pretend that it is not happening.
Next time you are in an (assumed) unfriendly situation, take a think and see if negative-positivity applies.