That is highly contested mind you.

https://roadsandkingdoms.com/2014/who-owns-chicken-tikka-masala/

The British attempts to claim chicken tikka masala for their own have been heard in India, and they have raised ire. Rahul Verma, a New Delhi street food expert, bluntly rejects the Shish Mahal story, claiming to have tasted chicken tikka masala in Uttar Pradesh or the Punjab earlier in the 1970s. Hemanshu Kumar of the website Eating Out in Delhi, has gone on record calling out the silliness of the designation campaign, and offered an alternative origin for the dish in a recipe from the 1961 edition of Balbir Singh’s Indian Cookery. And Zaeemuddin Ahmad, a chef at New Delhi’s Karim Hotel, which was established by the last Mughal emperor, Bahadur Shah Zafar, claims that his family invented the recipe for chicken tikka masala many, many years before all of this. The general consensus being that Sarwar’s Glaswegian campaign [to obtain European Union Protected Designation of Origin status for Chicken Tikka Masala] was anything from absurd to offensive and imperialist, pillaging South Asia’s culinary culture in a type of aggressive culinary neo-colonialism.

But the biggest problem for Sarwar’s campaign, and for any attempt to pin down the origins of chicken tikka masala to write it into the story of British food, is that the Glaswegian origin story is definitively a crock of shit. The real origins of the dish are incredibly diffuse. “Many chefs have claimed to have ‘invented’ [chicken tikka masala], but it was certainly not Ali Ahmed Aslam of Shish Mahal,” says Grove. “The restaurant did not open until the ‘60s and there was already a Glasgow claimant in the shape of Sultan Ahmed Ansari, who owned Taj Mahal and claimed to have invented it in the late ‘50s.” But more than just the fact that there’s an earlier Glaswegian tale of CTM [chicken tikka masala is so ubiquitous that it has its own acronym], the very story of the fussy patron and the tomato soup was pure drunken invention. “Along with Iqbal Wahhab, now of Roast Restaurant, I started the urban myth of CTM being tikka with added Campbell’s tomato soup and spices for a joke,” admits Grove. “Yet somehow it has become accepted as the official explanation the world over.”

Invented in response to persistent questions of "where's the fuckin' gravy?" followed by threats of mayhem.

British dish made by the Indian diaspora. The people matter as much as do the "elements".