Oh Freddy that's fascinating! My Hong Kong friend at University taught me quite a bit of Cantonese, and 'innit' could be translated into 'hai-mhai' (is/isn't it?) which is rather similar to the Hindi you mention.

But as a child in West London, we all spoke with rather a Cockney-type of accent, and I remember my father smacking my bottom for such utterances as, "It's raining innit?" But the 'innit' was only used strictly as a substitute for 'isn't it'. I love 'innit' when it's used for any and every kind of question or statement. It always makes me giggle innit!