In reply to AlisonSmiles:
Add me to the list of people who didn't really know what you were talking about in your OP (and I live a few miles from you and commuted all through last winter).
If my commute was what you described (which a good part of it is) there I'd be sticking to my winter/all year slicks (Sch Duranos), which I've just swapped off my cross bike onto my road bike wheels. A big chunk of my commute though is on the Middlewood way which can be a bit of a quagmire at times so I use Sch XC Pros. That sort of thing might be what you want (I got mine in SVC btw)?
I really can't conceive of how studded tyres can be cost effective in our winters (and I reckon we're going to get another wet/mild one, ha!). Icy conditions are just lethal really. 5 years ago I crashed twice on one morning commute, totally unpredictable black ice. First time slid 20yards in the middle of the road and the other time lost my front wheel, banged my temple, wrist, shoulder etc. Fell twice last winter too at very low speed, crashing onto my hip. Not worth it, get the train! Run instead?
Buying 700c disk wheels is a pain. There doesn't seem to be any choice and seem too expensive to me. Keep an eye on ebay though - sometimes people sell off newish sets when they're upgrading: Boardman, Giant - that sort of thing.