Quoting Rohan McLeod (rhn@jeack.com.au):
(Remember, if the kindly gentlemen of the constabulary ask you why you like privacy, the canonical rejoinder before referring them to your attorney, is to ask if any of their windows at home have drapes, and why.)
Since we live in a time of great controversy regarding the trade-off between privacy and national security; it seems to me the question should be: " Justify to me, precisely why you need to know ' this', in terms of your legislated task ? "; .rather than me needing to justify why I want privacy !.
Far be it from me to criticise, but I personally think my own way of making the point is more stylish. FYI, not sure what the applicable caselaw is in Victoria or Oz as a whole, but in the nationstate of my birth and residence, peace officers are generally under no obligation to tell subjects of lawful investigation / suspicion the truth. So, asking a peace officer to explain something to you is often pointless, as you may be told something either accidentally or consciously at odds with reality. Fortunately, in same nationstate, it is always lawful to tell an officer 'If you claim I _must_ answer that question, I'm sure you won't mind my having that claim verified by a magistrate in the presence of my attorney. Meanwhile, am I free to leave, yet? Until then, I'll not be answering any questions.' In the unlikely event anyone in present company is interested in the foreign caselaw on that point, the ruling case about non-custodial police encounters is Terry v. Ohio.