Thin Layers . Thin stuff that fits tight Snug . Winter cycling clothing under combats and or track suit or fleece works much better than overpriced hunting kit.
Pocket handwarmer . And a flask . I always find thin snug fleece or Roubaix type stuff that fits well keeps you warm but lets you breathe . Full zips for outer layers to allow ventilation. Portwest beanie hats with the led light are outstanding cheap light reliable and perform a two for one function. Insulated insoles are essential.
Pair o' tights and a change of socks...if ee wore lucky.
Edit: A better Yorkshire accent needed