This has been discussed on another thread jsut in th past few days, and the concensus was that they are a waste of money (as well as being illegal).
In some cases, the plates might even draw attention to you. FOr example, there is a "prism" type of plate that claims that the number is invisible when viewed from an angle as a gatso would. Even if it did work, and there is some doubt of that because the angle of view of the camera is wrong for it, if a police car passed you and glanced at your plate (as they do) it would attract attention by dipping in and out of view as he passed. You would most likely get stopped for having the illegal plate then.
There is more on cameras, detectors (worth a look at those) and the dodgy plates here
http://www.ukspeedtraps.co.uk/camerashy.htm It is quite interesting reading about the other tests they have done on cameras, guns and the detection equipment that you can buy.
Henry
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