In reply to Andy Hardy:
I swear by my Buffalo for wearing all day in cold weather, but it’s definitely not ideal as an extra layer- too heavy and bulky to mainly carry round compared to a Primaloft layer, say.
I use a Haglöfs Barrier III as my belay jacket in winter, works for me and is available at a reasonable price (£65 without a hood or £87 with, at a cursory google). Could do with a chunkier, two-way zip, but I can’t fault much else.