I was driving down a hill in Preston one winter. It meets up with a main road at the bottom which is pretty busy, so I hit the brakes and nothing happened. There was ice. I had to slam the damn thing into the kerb to stop, if I hadn't done that we'd have gone into the main road and got creamed by a Mini (I know that sounds unlikely, but my car is a Fiat Punto and therefore about as solid as a jellyfish made of cake).