You could do something different.
If it happens again (well you can dream) you could take pics of the car on your phone, make sure he knows you are doing it then if he asks you to stop refuse then make sure you take pics of his tyres, his brake lights, his insurance disc, tax disc and anything else that takes your fancy, the inside of the car and you can even take a pic of him too.
Once it is on a public road you can do whatever you want so long as you don't damage the car or him if he threatens to call the police let him, just make sure they see the illegally parked car.