Durham Leys Farm is located in the quite charming village of Marsh Baldon, on the other side of the green. It is quite easy to get to. Once you come off the main road there is a single track road with plenty of passing points. Go to the Seven Stars Pub and they give you detailed directions.
Basically it is a sectioned off part of the horse field. There are no showers or toilets so I think £15 per night is a bit steep. Waste dump and fresh water supply are perfectly adequate. The views are very good, the location is dead quiet. It might get a bit cosy with 5 caravans, but nevertheless enough room. The pitching area is flat and level.
Never saw the owner, just put the money in the box as requested. Not a problem. The location is very good to visit Oxford. The park and ride is fairly close. I would strongly recommend that it is used as Oxford looked a nightmare for traffic and parking.
The local pub, Seven Stars is very friendly and serves excellent food and Is easily walkable, make sure that you take a torch as you can lose your bearings on the way back as there is no lighting.
All in all a good site that is well worth a few days to visit Oxford and a couple of nights out in the local pub.