Well, unless you're fortunate enough to bump into an unattached farmer on his ten yearly trip to that-there-London or earn an absolute shitload yourself, you create a mental shield that is mostly only penetrated by direct threats and non verbal communication whilst simple physical proximity/personal space is unfortunately almost non existent. Or you go nuts.
The thing with people in London being unfriendly because we won't talk/chat isn't accurate - we're talking all the time. Just not necessarily verbally.
As a general rule, we'd really rather not be that physically close with anybody we're not intimately involved with, but the way to deal with it is through the less confrontational non verbal communication.
If you actually look at the behaviour of people in a very busy environment, you'll see that there is communication going on all the time - like Starlings know not to fly into the Starling next to them, people instinctively shift their positions slightly, pick up their bags off the bus seat next to them just from proximity - whilst there is apparent no eye contact, there's a whole load of being aware of exactly what's going on and interacting without having to say a word. We'll know that particular person is best avoided, that it might look close but there's plenty of time to get across the road and that driver isn't one of those whose right foot is ten tons heavier than normal (so won't lift off the accelerator onto the brake that easily), going by their road positioning and engine noise, that person over there is clearly unfamiliar with the area and might need to be told the connecting bus they need stops at the 3rd stop in the row, not this one, or will need a hand to get their shopping trolley off the bus as there's a big drop between bus level and the road at the next stop.
Urban design is supposed to communicate directions to people without needing to tell them (lighting, planters, road shapes, etc) like fencing can be used to shift livestock into pens - unfortunately, some visitors don't understand this communication, which is how you end up with the much detested London offence of stopping dead in front of me looking up and around with your mouth open instead of keeping moving at a normal warp speed and then stepping into one of the eddy sections.
Problems arise when construction doesn't take into account human behaviour - hence carefully designed crossings that aren't used because the actual natural route humans (and other animals) would take cuts directly across a corner or is 7 yards down the road and doesn't involve crossing a road, walking along, crossing at the crossing, then walking back on yourself and crossing another road, for example - blocking the line of sight to the logical route can discombobulate somebody not used to having things blocked, but is normal for somebody who is directed like that when getting out of a tube station all the time.
We don't have to like it and many people cope by not willingly going out unless absolutely necessary (thank fuck for Amazon same day and Ocado, as that saves a lot of stress, never mind the numbers that WFH), using headphones and generally focusing entirely upon getting from A to B without being impeded any more than necessary. Or they wait until they can sell up & move to the countryside expecting peace and quiet, only to find that it's full of smells and noise, church bells, errant sheep and combines going through at night. And lots of people who want to know who you are, where you're from and even if you're having a good morning when you're bravely trying to find your way to the shop on a non pavemented, winding road with gates, weird bits of wall and actual bits of houses sticking out into it of a morning.
Oh, and running/exercise. That's very popular for those physically able to do it, whether it's urban running at stupid o'clock, going out somewhere a bit greener just to get away or hiding in a nice, air conditioned gym where there are again a whole bunch of unspoken rules and communication - coping mechanisms to satisfy the fight or flight (always more useful than the freeze) response.