fog..
No, we keep on going at line speed, to keep time. Obviously if the rails are slippery, or leaves on the line, then those factors change the braking performance of the train; 417 tonnes on a couple of inches of metal rail, travelling at 125, when braking occasionally the wheels can lock up, and the speedo goes to '0', and it feels like an ice rink. When you know you're approaching a red aspect, with a junction in front of you, thats quite scary....!!!
As regards to signals, they are better now, as they are being replaced by LED singnals. Sometimes you cant see them though until they go past your cab.
I have to admit, i feel a great sense of pride, skill and a little buzz when its thick fog, night time, 125mph and you brake for a station, hit the platform at 60mph and stop in a trains length at a small marker saying 'HST Stop'.
Rather the same as the smoothest of landings in the worst of conditions....??