Well, they were British chefs with South Asian heritage who of course were indirectly here because of horrific Imperialism
But it is British, its very British. Despite what Farage and co want you to believe, we're a multi-cultural nation and have been for centuries.
British-Indian cuisine is at this point distinct and diverse enough from traditional Indian cuisine that it is its own thing. And its super widespread - even the racists discuss how shitty they are over a curry