Regarding your reader RB of Sutton Coldfield fitting winter tyres only to the driven wheels of his car, last winter I fitted two winter tyres to the front of my Auris. In snowy conditions I observed the rear was a bit unstable. This was later confirmed when coming out of a bend on a loose snow-covered surface at about 30mph, the rear began to oscillate slightly, corrected itself when I removed my foot from the throttle, then slowly spun through 180 degrees coming to rest against about three feet of snow at the edge of the road. I was fortunate that there were no other vehicles around at the time. I drove at a slower pace to arrange to get winter tyres on the rear.