I would say no, you cant touch them,even if he doesn't own the property they are parked on
I used to own a flat with a com car park and at the end of the car park was a garage which was rented by a local bloke,he was allowed access through our car park to get to his garage only.
we had a falling out, he bought a scrap motor and parked it, after refusing to move it i asked the plod if i could move it from my property,the answer was no,i would/could be prosecuted. a solicitors letter to the owner of the garage saw it disappear.