I think it's just a case of the Police being lazy, technically the owner has broken the law, I am sure this would be categorised as trespass which is an offence, so the police should obtain the details of the registered keeper and contact them.
It is on private land so a civil matter only. Trespass on private land is also a civil matter only. Hence police cannot actually do anything within their powers, as the police deal with criminal not civil matters in terms of the law. Sometimes our law really is as much use as a chocolate teapot
As it is on private land you DO have the right to remove it, although without causing any damage otherwise you are liable - but how could they prove you damaged the vehicle if you moved it to a dodgy car park with frequent car breaks, ASB ect...
Personally it does sound like it has been dumped, if left for a long while the police can but an abandoned marker on it on PNC, then wait a bit longer and the council will remove it.
But, you still have an abandoned car on your drive for a long time