Fog, actually. A rather warm and very wet one for the last 24 hours or so. Not terribly thick; I can see about 250 yd. It's low cloud, because places like Heathrow and Gatwick have only got a bit of mist. The air above the fog is even warmer and if it were to clear the temperature would shoot up to over 20°C in no time. It may happen tomorrow.
It didn't. It was just more fog, not terribly thick but we've now had 52 hours of it and everything is dripping. Previously invisible cobwebs are everywhere. Down at the pub, being 400 ft lower, they wonder what I'm on about. They always wonder what I'm on about.