Derives from the chav/townie/pikey sub-culture, but falsely over-labbeled on the British Asian Communities. Innit is a shortened version of is it not, in context, it would be "is it not?" which we can see is a question due to the required question mark and change in the pitch of the voice to indicate a question is being asked. Chavs, however, due to their lack of education (zero GCSEs) and ignorance towards learning English at school because "i already speaks it, innit", tend to, more often than not, use the term innit when a statement has been used, rather than a question.
Linguists and scientists have studied chav language and have determined the following:
1) they have tried to invent their own language
2) this is because they do no understand standard English
3) they use their "pikey-speak" to communicate with other like chavs
4) they speak in a pattern:
5) (noun), (obscene word), (verb), (subject), (innit)!
6) the pattern of speech repeats itself
7) the order may be altered according to IQ of the chav