Been doing a fair bit of online research since the week-end for solutions to this very issue.
My conclusion, guided by many different web-sites, blogs etc,, was to opt for Muckboots as a mid- to high-price quality range of footwear (as with quite a few other contributors to BFW) and, in particular, the Spey wellington, in terms of rugged design, sure wet-weather grip and, most importantly, warmth in severe cold conditions. Not forgetting the fact that the flexible neoprene wellington-style design allows for the upper part of the boot to be rolled down, when conditions improve to create an additional field-boot style.
I would have certainly gone for the Tay Sport as a first choice (also highly recommended) but sadly this style has been phased out by its American suppliers (unless you take size 3 or size 12 (!!), which are still showing as residual stock on some sites). It seems that the Spey is virtually the Tay Sport in all but name except for the trendy(?) camo design of the calf area.
Anyway, I ordered a pair on Monday (cheapest price I could find was £89.94 incl p+p while Amazon wanted £108!!!) ) and they arrived Wednesday morning, and they DO feel very snug and comfortable to walk in. Also, because of the triple-layer design (just order your normal shoe size) I only need medium style socks rather than thick, chunky thermal ones.
I'm out on the Derwent today hoping for a perch or two, so what better way to trial them now?!
Thanks to other contributors who helped me make my decision.
Roger