While it’s true the British came in contact with and ruled a vast variety of cultures I think it’s important to keep in mind that up until recently there hasn’t been a vast amount of people from those cultures that resided on the island. The common Brit in the 19th and 20th century might have been aware of spices and certain foreign delicacies but they wouldn’t have been exposed to a lot of people who actually had the ability to cook those dishes. Things are changing now. I think in 100 years British food will be way different as what it means to be British changes too.