It's an interesting point the OP brings up. He's in the UK like I am and I guess he's thinking about last winter which was freakishly bad for us. We don't generally get really icy/snowy winters in England, if we do get some snow it's usually just for a day or two and the main roads are kept clear on the whole. Obviously there are always bad side roads and we can get unexpected downfalls like anywhere else. That said, how rear wheel drive cars handle ice and snow does concern me. In fact when I think about my new motor it's the only little worry I have in the back of my mind.
I'd like to hear other opinions on winter tyres too. I'm also wondering if putting a bit of weight over the rear axle can help. And I suppose socks are always an option
http://www.autosock.co.uk/ A mate of mine used to live out in the Peak District and he swore by them.
:edit:
A quick look at the Autosock site and I could get front and rears for about £130
:edit:
Autosock don't seem to do a size for the rears of an M Sport. I read it incorrectly. However, Weissenfels WeissSock seems to have a larger selection.