Doesn't attaching the small low worth GPS device to someone's big and higher worth car make the combination property of the car owner? As in: He didn't steal it, they gave it to him. And he then moved it from his car to his house, totally reasonable.
It's called filing for title, and you do it through the DMV. I think the owner is notified to come move it, and if they fail to do so by a certain date then a title is issued to you. Google "file for title." I had a high school teacher that said he did it for a car that was left on his rental property when the tenant moved.
Edit: Just noticed the pounds sterling. I'm in the USA for reference.
In my case my private parking spot was used by a stranger and I blocked that car with my own car. My car was completely on private property doing so. I did block my neighbours car too but it was also a private parking spot and I had permission from my neighbour to do so.
The police officer rang my doorbell and ordered me to move my car, as blocking someones car would be an offence (disabling personal property).
I asked the officer to give the offending car a ticket but he couldn't do that as it was on private property and thus a civil matter. It was also not illegal for the car to park on my private spot as I don't have a gate which makes the apartment driveway an extension of the public road, and thus usable by everyone. Dutch law is complex.
I think the officer was wrong telling you it was mandatory to move your car. You cannot disable the offending car (e.g. calmping it would be illegal), but there is no obligation to arrange your private property in such a way that they could exit it.
He was probably confused by the rule that you are not allowed to block an exit ("uitrit") of someones driveway of proprety by parking in their way. But that rule does not apply if you're parking on your own private property.
