Livo,
as noble ox says there is a lot posted on the subject. i think bengali bob's three balti is good start.
in very simple. BIR = indian Bangladeshi, Balti = Pakistani. it gets more complicated as Pakistani is also BIR with Balti a very small sub set.
Pakistani is found in a few concentrated areas in the UK. Bradford, Manchester to name 2.
in general i don't like the Pakistani version. i've never really worked out why. i dont like curry on the curry mile as i'm sure it is mainly Pakistani.
i think the difference is down to greater use of methi and probably use of gm in place of mix. i also think the base must be different. bengali bob i think in exploring balti is working on other potential differences of which stock is clearly a factor.
as for balti the dish or method of cooking has nothing to do with the difference. i in fact believe contrary to popular belief that balti is best cool fried not hot fried (which i use for BIR).
the trouble is many Indian BIR have attempted to copy Balti and now the waters are very muddy. the real McCoy though has not traveled outside Birmingham.
the type of naan bread is also a good indicator - balti is quite thin and sort of crispy. indian naan is soft and doughy.
there is a BBC lenny henry video i think on youtube that gives a real good overview. may even be link on this site.
https://curry-recipes.co.uk/curry/index.php/topic,12060.msg96944.html#msg96944