Its not so clear cut: https://www.northcountrypublicradio.org/news/npr/1145119758/who-created-chicken-tikka-masala-the-death-of-a-curry-king-is-reviving-a-debate

"It's kind of like: who invented chicken noodle soup?" says Leena Trivedi-Grenier, a freelance food writer who probed the various origin claims in 2017. "It's a dish that could've been invented by any number of people at the same time."

"How do you colonize and enslave an entire country for a century and then claim that one of their dishes is from your own country?"

Still possible it was created by the South Asian diaspora in Britain but there's a reason the likes of Nigel Farage want CTM "remigrated" and not so for the likes of Shephard's Pie or Yorkshire Pudding.