I had this problem before and I almost got arrested because someone left a scooter on my parking spot for 10 hours and I went there to put a lock on his scooter, but some police officers just came around the corner and saw me trying to put the lock.
They said I could be arrested for criminal damage if the scooter's owner said that I did any scratch to it and the only reason they were not going to arrest me is because I had reasonable cause to be doing what I was doing, I even left a note with my mobile number.
I asked what could I do in this situation, they said basically nothing you have no rights to intervene with a vehicle, the only LEGAL thing that you can actually do is block the guy in and if they try to do something to your vehicle than you can get them done for criminal damage.