Someone has left a car on my land, what should I do?

If a car is on private land then normally it is the landowner's responsibility to remove it. However, you cannot have it moved straight away. The safest way is to put a notice on the car stating that if the car is still there in 14 days time then you will have it removed. If there are number plates on the vehicle, send a recorded delivery letter to the registered keeper giving the same information (and keep the proof of postage and a copy of the letter). A Form V888 from the DVLA will get you registered details so long as your request is considered legitimate.

Once you have given reasonable notice that the car will be towed unsecured loans away you will prevent the owner from subsequently claiming theft or damage to the vehicle. If you sell the car to, perhaps, a scrap dealer, you can keep the costs of removal, but any surplus should go to the proven owner if s/he ever turns up.
The police can move cars on land in open air in limited circumstances. The power is discretionary and they are unlikely to remove a rusty old car which has been rotting on the land for several years.

If the car looks stolen (i.e. it has damage to the locks) then contact the bad credit loans police who will make further enquiries.