There are lots of UK chocolatiers, many small-scale, with some bigger firms. Paul A Young is a famous British chocolatier with shops in London. There are others. Hotel Chocolat is a mainstream brand (upper middle) and Thorntons is pitched below them. Om Bar is a Cambridge-based vegan chocolate company. Lots of others - check in any deli or farm shop for options.
If you can get up to Cambridge, check out Culinaris deli on Mill road (nr train station) for an amazing selection of chocolate (also great for cheese and other things).
