I'm going all in here.... I have come to consider that the longer serving are more likely Bangladeshi Restaurants, which also in my opinion, serve generally better cuisine. Or at least to my tastes anyway. So I would lean towards saying that the recipes originated from there and are a mix or various regional dishes from India.

However, since the British Indian Restaurant appears to be fairly unique in its flavour and cooking methods, i'd have to answer that they come from Britain.

This is a brilliant post and explains something I said badly before.

The BRITISH palette.

That is why I think you'll find as you go down this cooking road that all is not what it might seem compared to a typical home-style recipe and yet it is in foundation, basically the method of cooking meats and spices.

This is why I've followed that traditional style and to be completely honest in some cases actually prefer it, though I do miss the oils.

Nice one. Anyone else?

My home city of Dundee has a very low Asian population compared to other English towns of a comparative size, e.g. Coventry. The largest "ethnic" are Pakistani/Bangladeshi and it is they who own and work in the majority of takeaway and/or sit in "Indian" restaurants. It is therefore a curious misnomer, technically, to describe this food as "BIR". Back in the seventies I can remember takeaways having signs that said "Indo-Pak" cuisine.

I don't think I've ever seen anything other than white customers in these restaurants though, and therefore I assume (as is the conventional wisdom) that BIRs exist, in the main, for Caucasian and not Asian customers. This cuisine could then be assumed to be unique to the UK, and not reflective of the cuisine of the origin countries.

I wonder, if like a lot of things, BIRs grew throughout the UK from a starting point in London? I know that there is some evidence of curry houses like Veeraswamy serving food there in the early 1900s.

I've just finished reading 'The Heart of the Matter' by Grahame Greene which is based in West Africa during the 2nd WW.  The cooks are Indian and curry is mentioned several times in the book but sadly without a recipe!  Obviously colonial Britain made use of the best food to be found in the colonies - curry!

"Neither of them had any appetite for lunch, but the
cook, who wanted to rise to the occasion, produced an
enormous curry which filled a washing-basin in the middle
of the table: round it were ranged the too many small
dishes that went with it the fried bananas, red peppers,
ground nuts, pawpaw, orange slices, chutney."

This makes for a very interesting read:

http://www.hub-uk.com/interesting/curry-history.htm

Which was written by Manju Malhi http://www.manjumalhi.com

She's got some nice recipes on there, certainly up your street Mikka.