There are a lot of regional foods in the UK, so it makes sense the non regional foods all end up on top, though in reality the non regionals probably are not most popular anywhere.
Chicken tikka masala was invented in the UK, and there's a lot of discussion over whether it was made in Scotland or England by immigrants from India.
It seems it has a bit of an unknown origin, but I can't imagine it existing without westernizing South Asian ingredients by way of British India. I'm not a historian by any means, but I guess I liken it to American Chinese food, which also has a bad rap due to harmful history as a result of westernization.
Yeah I'll be in the lookout for specialty shops and not just grabbing it randomly from a menu somewhere, just to make sure I get an accurate experience.