My take
The landowner has the rights over access to the disused airfield but not the rights over the air above it. Yes the aero club would need permission to land and yes the model fliers would need permission to access that land
But I don't think the Aero Club would need permission from the landowners to descend over that land.
So SRD I think you are correct that with permission the model fliers are legal but the aero club do not need permission from the landowners
Pace