ADR 17 - Fuel System
The function of this Australian Design Rule is to specify requirements for 'Fuel Systems 17/00' using 'Liquid Fuel 17/00' other than liquefied petroleum gas that will facilitate safe operation and reduce the risk of fire due to fuel spillage during filling operations or as a result of impacts.
I couldnt find anything that was relevant to Passenger vehicles but on heavy vehicles you are not allowed to relocate shorten/lengthen the fuel filler unless its certified. Now im assuming that something similar will exist for passenger vehicles, something to do with impact, lessening fuel spilling in case of an accident etc etc.