I have to say, I find this all very foreign. Maybe I'm going to the wrong places, and certainly there are people who do the low trackies and baseball cap thing (though I can't say I've seen the socks tucked in! What a shocking look!
), but they're definitely not in the majority or even a large minority in my city. Most people just wear normal clothes and listen to whatever they want and are friends regardless. At uni there's a wide variety of styles and types of people and you'd be hardpressed to pick out specific groups of people by what they're wearing.
I'm wondering what the situation with school uniforms is in Britain? I know Epona said that this is not just a young people thing but people in their 20s too, but I'm thinking perhaps it starts in high school; that's where most people find their circle of friends, though of course it does expand and morph when you leave and go elsewhere. But in Australia nearly all schools people wear a school uniform, whether they're public or private schools. Which I really think eases a lot of the money/style distinctions that seem to be happening. You don't really know who is well off and who isn't because everyone wears the same thing, even things like shoes don't really give you a clue because most expensive brands don't make black leather school shoes. And while there were definite groups which you could probably categorise it would have been much more difficult for me to have identified what type of music for instance specific groups would have liked at my school.