Found this road in the Northumberland National Park running north from Cawburn towards Stonehaugh in the Wark Forest part of the larger Kielder Forest.
Where the public road ends at the southern approach to this road, there's a big sign and a gate saying unsuitable for vehicles.

Unsuitable is a clever word, I suspect most people read that to mean, vehicles prohibited. I just assume it is meant to deter people from driving these roads with fearsome suggestions of potholes, ruts, mud-filled puddles and maybe even ranging torrents. But in the spirit of adventure, I take the view, why not give them a go.
This turned out to be a great road, yes full of potholes, massive puddles, deep ruts and mud but easily passable in a 2WD car even after incessant rain the night before.
The road is part of the National Cycle Network route through the park from Hadrians Wall towards Kielder - thoroughly recommended by car, bike or on foot.
There were a numer of wallsteads along the route, very reminiscent of some roads in Donegal Ireland with lots of abandoned houses.