A public footpath, bridleway etc. do NOT count as "highway" for the purposes of this offence. The 50 feet law is probably the most misunderstood, misquoted piece of shooting legislation (and it's not even from any of the firearms acts, but the highways acts. Also, note that the legislation says "without lawful authority or excuse". I don't know if there is any guidance as to exactly what that means. Do you need to have lawful authority to shoot near the highway, or is the lawful authority or excuse related to the "endanger, interrupt or injure" part of the offence?
the bit about lawf