I’ve found out that in NSW a vehicle parked on private land can not be legally wheel clamped, impounded or towed away except by the police. This is really quite annoying as the police are generally reluctant to act in such circumstances and the land owner is left with few practical options to deter such behaviour.
Perhaps towing companies were in the past being a bit too zealous in terms of the conditions for the release of impounded or wheel clamped vehicles. However these restrictions don’t seem to get the balance right either. If somebody parks their car on your private land and it is clear from signs or other indicators that the land is private then there should be a legal, timely private means of dealing with the offending vehicle.