koam,

I'm sure that it pre-dates the emergence of the Chav. I doubt that it's particular to them, as that particular subculture has drawn its language from a combination of American films, Jamaican vernacular and text-speak.

You are probably correct in thinking they are yet another wave of the same subculture, somewhat akin to the old "bovver boys" judging by the use of language and lower educational level (not necessarily by nature - I feel that a lot of them have based their lives on "Idiocracy")

And indeed, "half ten" does mean "half past ten". The past has slowly waned in common usage over, I would assume, the last 30 years. I certainly remember using the clarifying "past" when I was young.

As to whether "o'clock" means "of-" or "on-" the clock, I will leave to those with more knowledge than myself. Neither seem overly elegant to my ear, perhaps it's a throw-back to Middle-English?

As a hopefully fairly literate Brit, I was taught that the correct form is "think of". To "think to" strikes me as an attempt to think in the direction of something rather that having thoughts on a subject.

In a similar vein, I've been somewhat bemused (and amused) by the American English usage of the phrase "quarter of the hour" as opposed to the British "quarter to". Hearing "it's a quarter of ten" makes my mathematical mind imagine that it's two and a half.

And what kind of people use it over here... http://www.urbandictionary.com/define.php?term=chav