I'm not convinced you're allowed to cycle on this path. I didn't notice any signs and the gates on it are fairly inconvenient if using a bicycle.

Is Grand Avenue fully accessible by motor_vehicles?

I changed it from a tertiary road down to an unclassified road. It is probably nearer a service road with appropriate access rights.

Are there really this many tertiary roads all around here?
I suspect most are narrow unclassified roads.
Probably might be able to tell from aerial imagery.

Is this really some kind of 'road' maintained by the council?
On OS Streetview and even old OS maps, they show it as perhaps some kind of track.