The Great British Weather

your arteries are well away from the external parts of the body. when its cold you boy will stop circulating areas to conserve heat, your blood won't get cold.

In the short-term surface (skin) capillaries actually dilate when they are exposed to cold, rather than shut down as Ed suggests (in an attempt to keep the skin oxygenated) - hence why you get red cheeks and nose (or lobster pink legs) in frosty weather.