London Visitor Advice Being FriendlyBeing Friendly
Ah yes - the British reserve. It is alive and well, but don't mistake it for unfriendliness. 
'Leaving people be' is big for the British, but once you get chatting, they're generally a mischievous, fun-loving bunch. If they didn't like to go out and socialise, they wouldn't build a city like London. Being able to laugh at yourself is an essential part of the national character, as is, not taking yourself too seriously.
The power of politeness should never be underestimated, or interpreted as a sign of weakness. It's a form of protocol with a challenge/response code. Often if a Brit talks about the weather, they're sizing up your manner, not what you're saying. Can you return the banter? Do you regard the conversation as a springboard to promote and publicise your own talents? Are you understated, but confident in your opinions? Can you return the politeness? It's amusing to dissect - for example. Here are two Brits on their way to lunch.
Brit 1: Do you want to tag along?
Brit 2: I don't mind if I do.
Here, despite the sentence making questionable sense to a foreign observer, the correct challenge/response politeness has been served.
If you see people meeting in London you'll often hear the phrase "All right?". The usual response is something along the lines of "Hmmmm, yeah... not bad." It doesn't make a great deal of sense, especially to the average American visitor. What these challenge/response codes are really about: is not being seen to be too keen.
There's a quote by [the typically downbeat] Nietzsche "The lonely one offers the hand of friendship too quickly", which sums up this reticence neatly. Brits are fine at being friendly, they're just initially cautious - because they're aware that the friendship they offer is being evaluated on how easily it is given. Is it worth anything, if it's just handed out to anyone? Probably not. So this apparent coldness, actually serves a purpose.
You will always meet people in every country you visit who have no interest in talking, or being friendly towards visitors. But just ignore them and move onto the next person. No one likes them anyway.
