In reply to KarlH: Thanks so far all.
I am using a roadbike with mtb type pedals (so that I can use my "biggest" shoes)
I am also using Endura neoprene overboots.
On my bottom half I am using a pair of running tights underneath a pair of "ronhill tracksters", plus cycling shorts.
Interesting that someone suggested ensuring my calfs/lower legs are warm.
(My legs feel warm enough, but insulating them more may help my feet !!
Keep your ideas coming folks