Government has announced it will be making them illegal in this country, together with devices which forewarn you of the position of gatsos by other means.
As a student in London many years ago, I used to listen to them overnight for entertainment value on a regular FM radio. Normally you could only hear one half of the conversation. At that time, listening wasn't illegal, but making use of any of the information was. When I picked up an armed robbery in progress just around the corner, I did let the building security know, and they locked the front doors. I suppose that was illegal...