While radar speed camera detectors may still be legal at home – the 2006 Road Safety Act did include enabling provisions allowing the Secretary of State to make regulations to prohibit them but this hasn't been done yet – the position is different abroad where many countries have laws in place banning the carrying or use of these devices.
For some years now it is has been strictly forbidden under article R413-15 of the French 'Code de la Route' (highway code) to have a speed camera detector in a car in France, regardless of whether or not it is being used.
Penalties can include fines of up to €1,500, confiscation of the device and of the vehicle.
Until recently this legislation didn't apply to satellite navigation or other GPS-based systems capable of displaying fixed speed camera locations as points of interest (PoI).