"If you don't have a "no parking" sign on your drive, he is legally allowed to park there,..."
You really need to get your facts straight, spathi !!! Don't you think, if that were so, that everybody who has trouble parking at their local railway station or simply begrudges the parking fee at the station car park would simply park on on the nearest front driveway they could find?
"...the police can do nothing."
Though there you are correct. Trespass is a civil matter.