Here's an extract about the expression innit:
By the end of the 1980s, innit — the unvarying question tag put on the end of sentences and used separately as an exclamation of agreement, “Innit!” — had become identified especially with black-British and later Asian-British speech patterns. So much so that, in the mid-1990s, my students at King’s College London were referring to their Asian fellows collectively as “the innit crowd”; and when Sacha Baron Cohen’s comic character Ali G parodied Asian and white “wiggas” (imitators of black styles), innit was incorporated in the title of a 1999 collection of TV shows. Since 2000, innit has been seen as one of the most recognisable features of “Hinglish” — south Asian English — and of multiethnic youth dialect, supposedly a new accent and vocabulary common to younger speakers across a range of ethnicities and mainly urban environments, which may eventually influence mainstream English. It is also seen as emblematic of the troublesome underclass known as chavs, and in 2005 jokes were circulating playing on the fact: “What do you call a chav in a box? Innit.” And: “What do you call an Eskimo chav? Inuinnit.”
And here's a link to arch-prescriptivist Lynne Truss's rather sniffy review of it.