If you've already got the wellies to cope with our snow that quickly turns to slush, but need the warmth then your best bet is a pair of Hunter's socks for inside your wellies to keep toes warm.
My insiders tip is a good old ebay seller Country Attire, after all ebay is practically high street these days. Of course the downside is the fact the snow plus Christmas will preclude a swift delivery but you plan ahead for future cold times or country walks.
I'm fully appreciative that welly socks are hardly the most exciting wardrobe item but due to snow I would have to say this is the one December I've not even bothered to peep in store. I nipped into Harrods for some last minute items and a Chanel nail polish on Thursday but that is it.
Update the 12 noon scenes around me 14 miles south of Central London to give it some perspective. You'll note how handy welly socks are and I did get mine from Country Attire on eBay. The picture quality is pants as it is my 3 year old blackberry which I must upgrade!
You can tell it was a blizzard due to how the snow has covered the tree trunks