I bought some of these geekish things that you slip over your shoes like mini crampons and you don't slip on ice unless you put the heels down first. There's a spiral which digs into the ice. I used to have some with little spikes in but I can't find them so bought these from QVC for 99p, on special offer in our outlet shop.
You have to be careful not to slip over in shops with tiled floors though! You would feel a fool slipping on a floor, when you've just walked a half mile on ice!
They're brill