One year Gilles (bless him where is he?) and I visited a field which he had identified and he'd spoken with the owner, with a view to having a CA camp-site. It was just a field, the owners lived opposite. We proposed showers, bogs, courtesy buses etc. Also a mowing and try to flatten out the molehills a bit. The logistics and cost of setting that stuff up for what is really only a small number of people was huge. And,as said above, most people have their preferred camp site and were not willing to move.
The field was ummmm... turn left out of MB, at the roundabout turn left, shortly after going under the bridge it was on the right. That's probably about as close as you will find a suitable private area. BSJ distance...
