Surveyed today, this lane is accessible to vehicles, I drove down it today in a car and even saw a delivery panel van emerge from it. 

There is however, a "Not suitable for HGV's" sign next to it, which makes sense because it's so narrow that if a vehicle and a pedestrian were to meet in the lane, there would be no room at all for a pedestrian to stand to the side of it to allow the vehicle to pass. I don't know how to map "no HGV access" on the map, so I'll leave this note open until I figure that out.