Once an event that endangers the aircraft is reported several government agencies become involved. They will probably include the AFP, ASIO ,ATC and the Department of Infrastructure and Regional Development. There are strict powers of incident and control compliance which empower the secretary to direct an aircraft both in the air and on the ground as they deem necesssary. On the ground the police would be running the show. Unlawful interference is a criminal act. The police and various bodies are now in control.
None of that overrides CAR 224 though. They can pull out all the authority they want to tell you to divert to XYZ airfield but if there is forecast fog or some other issue, you are quite entitled to refuse.
Same applies on the ground with engines running. The Police can say what they like but if the PIC wants to shut down and evacuate and that's what's going to happen.
The pilot in command shall have final authority as to the disposition of the aircraft while he or she is in command and for the maintenance of discipline by all persons on board
The 'Powers at Be' absolutely hate this little piece of legislation, as was evident during the whole 'who can sit in the jumpseat' saga at the 'Senate Inquiry' however the law is the law.