Can anyone recommend me a good waterproof winter boot for use with flat pedals.

Wellies.

Do you want them to look like cycling shoes/boots? In which case these (Shimano MW81):

Or walking boots? In which case these (Shimano MT91):

But if you really don’t want SPD compatibility and are happy with a bit more flex in the sole, these (Merrell Moab Mid):

Or if you want to look rad and freeridey, none of the above.

5/10 exum guides.

I just use my Scarpa SL’s. very waterproof and stiff too. A proper winter boot that sticks like a 510 to my Flatboy pedals.

Thanks for the info. Might try find a pair of Exum Guides.

Seal skin socks work well

sealskinz socks and karimoor walking boots from sports direct @35quid.cosey and dry