An Update to my Update:

Yesterday morning we were driving to the station: the same dark windy country lane we travel every day to work... there was a runner on the other side of the road (the correct side since there's no pavement, he was quite rightly in the road).

Obviously a healthy type jogging at 6.30am, the irony of his lack of attention to being seen and therefore being safe at all clearly lost on him.  Sure the paramedics would comment on his great muscle tone as they dragged him in to the ambulance!

The point to this? for heavens sake, wear hi-viz, be seen, be safe.

Riders, even if it's not dark, if a car can see you even a few seconds earlier, it could save your life, and that of your horse too since in all likelihood the car would see him before you.