Lasers don't emit too much sound so it shouldn't be very loud . Welcome to LPF. Advice from one noob to another: USE THE SEARCH BUTTON ! I just searched "United Kingdom" and this was one of the first posts:
Are you asking if they will get through customs? \i dont see why not as my 50mw green from ledshoppe arrived OK. If you are asking are they illegal to owm/use, then I dont know, but if you don't do anything stupid with them I dont see there being a problem.
I think I read somewhere that if they are being used as a laser pointer for presentations then they should be less than 5mW.