Year old thread but here goes: my 2004 XJ-8 (USA) has rear fog lights and I use them judiciously when we have heavy rain, mist or, of course, fog covering the roads. We're at the base of the Blue Ridge Mountains in Virginia and are subjected to fog quite a bit. Not surprisingly, a lot of knuckleheads drive in that stuff with no lights on, period.

As someone has mentioned the rear FLs are great for signalling to tailgaters to back off. Now.