Is this a guillemot and is it unusual to see it on a British beach in winter?

This bird was on Whitby beach this morning.  It didn't move even when we went quite close to it.  It didn't appear to be bothered by our presence and simply continued to preen itself   The tide was coming in and each time the water caught up to it, it simply waddled forward and then started to preen again.  We know it's a type of auk but which one? We're veering towards a guillemot but we didn't think they were seen in winter or on beaches.  Can anyone tells us if it is a guillemot and where they usually overwinter.