Another vote here for Nokian - their WR G2 tyres are designed specifically for slushy snow conditions which we get most of the time in the UK.
Others may be better in full snow conditions but I would rather have the right tyres 80% of the time than 20% of the time.
Four tyres are better because just as chains are only as strong as the weakest link, you won't stop as well if the ABS is controlling sliding back tyres in heavy braking. Having said that, you could make use of the traction of front tyres only, and not cane it round the bends, and from experience you will probably not notice the difference - you just won't be getting the best out of the winter fronts. Depends on how you choose to drive.
If you are happy with part-worn ex-German market winter tyres (6mm tread depths typical) , I can recommmend Online Performance Tyres in Alfreton Derbyshire who have an eBay shop, and for new tyres try Camskill Tyres.