"Only in relation to a declared terrorist incident"
Ah, I think I see where this one is going.
IIRC, and I forget the legislation under which this applies, in the UK certain ranks (Superintendent?) can authorise greater powers for their officers over an area for a period of time (again I apologise but I forget how long, it might be up to twenty-eight days). Powers might include things like a greater ability to stop and search people and vehicles, set up roadblocks etc.
I think this was intended to counter serious crime believed to be in the planning, enable searches for escaped prisoners, and to deal with anticipated disorder, unauthorised protest marches etc etc
There are apparently some areas of the UK where these orders were renewed as a matter of course so that in effect they were (are?) continuous. I seem to recall a program on this on the TV some while ago causing a bit of a scandal that shortly was forgotten.
Given the current spate of misguided nutters "driving elsewhere than on a road" and using people as soft bollards, should this sort of thing happen down under I would expect that this could be justification for these powers to be used by the police there in a similar way and then subjected to "mission creep".
Its a shame as I understand the need for such powers where appropriate but given that in the UK you can be convicted for terrorism for dressing up as Batman and climbing on a ledge to protest about bias in the family courts, rather than in the days when a proper terrorist inspired, well, terror (not that I advocate such actions) by making things go bang, it does seem to rather devalue the distinction.