You’re right that people import Teslas from overseas—U.K. Teslas are made in China. These Chinese-made Tesla models are said to be of better quality than the American-made models, so it makes sense that U.K. natives might prefer to get their vehicles from another country.
While Tesla did briefly entertain the idea of building a factory in the U.K., their newest gigafactory will be revealed in October 2022 in Australia. This will be the seventh Tesla factory worldwide—pretty impressive, particularly for a company not even 10 years old.