I agree with Nige, that rear fog lights are misused, but do see the need for them, in both fog (not light mist) and torrential rain. If you are being dazzled by the foglights, and your windscreen wipers can hardly clear the rain from the windscreen, then slow down and drop back from the car in front, because you are obviously too close to him, for the current conditions. Imagine if there was 100 yards visibility, and the traffic ahead had stopped for some reason. If their lights were off, then at 70 mph (or higher), you would just go straight into them. If they were all lit up, then you would see them, and be able to react accordingly. Most accidents are caused by speed, and failure to react to a situation. Don't make it more difficult by making yourselves invisible.