If anyone is having trouble with snow and ice, these slip-on gubbins are great:
http://www.amazon.co.uk/Petzl-Spiky-Plus-Anti-slip-Over-Shoe/dp/B000YB8SDQ
http://www.outdoorwarehouse.co.uk/index.cfm?action=shop.detail&pid=DDC2CD88-FF29-08BD-48EA8C02A3D2B051
The Microspikes are more hardcore, you could run on snow and ice in these, but they arent so good on bare pavement. Spikys have much smaller points so you still have to be careful, but you can walk indoors on them (avoid wooden floors!) and arent so cumbersome on pavement.
I have no financial links to these companies, but am a bit of an evangelist as they saved my butt many times last winter :)