It's so British that it's been called the National Dish of England! The key issue is that the dish was developed in England, for an audience of English diners.
>"It's so British that it's been called the National Dish of England!"
Come on man, that's just a marketing thing, it doesn't have any genuine cultural significance.
>"The key issue is that the dish was developed in England, for an audience of English diners."
You're ignoring my questions. Does the origin of the chefs hold no weight in your mind?
Furthermore, I'm British, and I've had plenty of curries in my time. Tikka Masala does not stick out amongst curries as something particularly different to the rest, and if there was something 'British' about it that difference should be noticeable.
It's the same thing with NYC pizza, there's basically nothing that sets it apart from pizza found elsewhere.