I've often heard the phrase "you lot" in British programs on PBS (for example, "Oi! You lot! Shift y'selves" or thereabouts) and have sometimes wondered about its origin and how it gained currency. It seems both elegant (short, easily understood, and accurately expressing plural of "you") and crude (on PBS, only heard in broad comedy) or perhaps colliquial. Its use seems to have sharply increased ca. 1960.

Why the increase, or is it an artifact of the corpus?
Do "you lot", "you-all", "you guys", as mentioned at the middle of Wikipedia on "you" qualify as cognates or is there some more appropriate term for the group?