Hi Richard, It's good to be able to talk things through. If I may first explain something, OpenStreetMap is not actually a conventional map. It is a licensed open database from which anyone can compile a map. Amazon has  its own proprietary mapping software based on OpenStreetMap data, which includes GPS technology supposedly to assist drivers in finding the most efficient routes to customer locations. It is Amazon's incorrect use of OSM data for their routing algorithm that often causes problems. I can assure you that OSM always strives to have verifiable ground truth in its database that, if used properly should cause no trouble. 

The track is now tagged with access=agricultural and motor_vehicle=no which means agricultural use only, no other vehicles. I've tagged the gate with access=private
and motor_vehicle=no. These tags properly interpreted mean no vehicles should approach from the A143. Lastly, is the gate locked, if so the tag locked=yes could be added to it?

Regards Bernard.