It is legal to produce, stock, sell and have adblue emulator in your possession, but it is not legal to use it in your vehicle on public roads here in UK as well as throughout the EU. By using adblue emulator driver and the operator will be breaking the law.
There are plenty of legitimate uses for adblue emulators and other emission cheat devices – agricultural transport, on-site construction machinery, vehicles operating or being exported outside of EU and many others… However, it is against the UK Law to use any emission cheat device in the vehicle, which is operated on public roads.