"Authentic" British dish...

...is Chicken Tikka Masala, according to British politician and former Secretary of State Robin Cook !

As one popular legend goes...

it was created by a bemused chef at a Bangladeshi restaurant in London, when an obstinate customer insisted that Tandoori chicken be made with gravy ! He just dumped a can of Campbell's tomato soup all over it and cooked it a bit and returned it to the delighted customer.

Here's the "official" description, as much as there is one...

Chicken Tikka Masala is Chicken Tikka in a masala gravy (commonly referred to as a sauce). There is no standard recipe for Chicken Tikka Masala, but most are variants of a tomato gravy (using puree or even ketchup) with cream or coconut cream and various common spices.

Apparently, it has become so "Indian" that almost every Indian restaurant serves it worldwide (well, except maybe the vegetarian ones), and is supposed to have replaced Tandoori chicken as the flagship Indian dish, although, obviously not of authentic Indian origin! Well, I guess that Indian techniques went into its preparation, but you know what I mean...