Old Channel 4 Drama

[Grimmore]

I was wondering if anyone out there knows the name of an old drama on Channel 4. The first episode started off on a train, where a woman releases some gas into the carraige. It turns out it's sleeping gas, and she has saved the people on the train as on the surface of the planet, there was a meteor shower or something as everything is very post-apocolyptic. The drama was then about the survivors venturing out into the world, not really knowing what just happened... Does anyone know the name of this drama? It was on quite a good few years ago, 1996 maybe? Would be a huge help, thank you!