What is the name of this tv mini series?

It starts with these people that are in a subway train car and there is a human species ending event. Their train crashes but there is an oxygen tank that explodes and freezes them all. When they wake up they are the only humans around. There is no bodies or people anywhere, and so they walk around the countryside trying to find out what happened. I think they do meet some people along the way. I thought the show took place in the UK, it may be a BBC mini series. It played in 1998/1999. That's all I can remember.