Sounds a silly question, but are snowboots tough enough for long periods out in the snowboots or perhaps to walk through deep puddles? I've used wellies in the past and want something warmer, but they have to be able to cope with walking through 2/3" of flooded pavement sometimes.
horrible horrible name but google BOGS boots. They come from the States and it is what lots of people back home (Canada) wear.... Warm to -30 or something and totally waterproof. There are now Uk distributors.