It's a civil matter between you, the landowner, the scrap man and whoever now has it. All you can do is attempt to sue whoever bought it for the return of the van. If the van was not SORNd then there may be repercussions on you from the DVLA. Assuming it is SORNd then you should make it plain to the DVLA that you are still the 'keeper' of the van and you do not give your permission for the registered keepership to change. The DVLA cannot then successfully prosecute you for failing to notify a change of keepership. However, you should bear in mind that if you left the van on another man's land, he can demand storage fees from you, and if these are not forthcoming he could sell the vehicle to pay them.