Foglights

Foglights are not something you switch on to let the person behind know that you know it's foggy. They probably already know. The grey, dank, low cloud obscuring visiblity probably gives it away.

They're meant to be put on so that people a long way back see there's a car up ahead from further back.

However - if there is a queue of traffic, making its way cautiously along in the fog, there's no need to switch on your rear foglights unless you're the last in the queue!
If you do, you just make it very uncomfortable for the driver behind, who has to follow you, trying not to be dazzled by your foglights.

Basically, if you can see a car behind you, switch them off!

The rules say:

"You MUST NOT
a: use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists and horse riders
b: use front or rear fog lights unless visibility is seriously reduced. You MUST switch them off when visibility improves to avoid dazzling other road users"

Please note that point b doesn't say you should use foglights if visibility is seriously reduced. It says you mustn't unless it is. There's a subtle distinction.

You can argue in the comments below.

I'll save thoughts about front foglights for another day.