A looong time ago gazza, but not any more.
In 1989 Australian Design Rules (ADR’s) were introduced which affect the construction (and import regulations etc) of all things automotive, including any Capacity Ratings of vehicles including towing limits, which are set by the manufacturer, or possibly the importer if the manufacturer has not specified such.
There were probably a few years grace, but compliance of these ‘Rules’ has been required by Law for a very long time.
In late 1998, agreement was finally reached by all State Ministers of Transport to implement National towing regulations. NSW's tow limit of 150% of the vehicle mass (or whatever it was), went out the window at this time.
Cheers
Brendon
Note to self: Don't argue with an idiot. They will only bring you down to their level and beat you with experience....