In reply to MrToffee:
How much do you want to pay, and how cold do your legs normally get?
Regatta do a nice 'soft shell' winter walking/mountaineering trouser in black which would certainly keep my legs warm in winter.
Decathlon sell Simond mountaineering trousers with inbuilt gaiters, removable braces, crampon patches and ventilation zips for next to nowt and I use these in winter.
Post edited at 13:33