Very difficult to find definitive clarification on whether they are legal or not. According to the law the plates have to be made of "reflective material" but doesn't actually state what they have to be made of. There is debate as to whether painted or wrapped metal constitutes made of a reflective material. Basically as the other posters have said as long as you get "legal" ones with the correct markings and fonts etc I doubt you will ever have any bother but basically its all down to the copper who pulls you over, there's good cops and bad cops.