Last time we had really heavy snow in Kent I had to drive along the A2 towards London. Queues of cars, and braking caused the car to veer one way or the other. I found that if I applied the parking brake the car was far more controllable. It was bad - took 10 hours to get home and it usually takes about 45 minutes. Watched a couple of films on the iPhone to pass the time!
Next day I decided to work from home....
Another trick is to get 2 strips of old carpet, about a foot wide and 4 feet long. Punch a hole in one of the shorter ends, and thread some strong cord through it, and tie the other end of the cord to the back of the car (choose something that won't pull off). Then put one of the shorter ends of a strip under one back wheel - same with the other back wheel. Carefully drive off - wheels grip, and carpet tows behind...
Works for mud, but haven't tried it in snow.
Don't blame me if you pull your back bumper off!! You have been warned...
(Obligatory warning, just like they put on coffee you get from takeaways 'warning - this hot coffee drink is hot'!)...
Orwic