Discretionary and Mandatory Exclusions
Rules of Evidence
Evidence Obtained Improperly or Illegally
Any evidence which was obtained in a manner that contravenes any Australian law, or by ‘improper’ means, may be deemed inadmissible under section 138. Also disallowed potentially is evidence obtained ‘in consequence of an impropriety or contravention of an Australian law.’ Inadmissibility is not automatic, but follows consideration as to whether reasons for admitting it outweigh the reasons against, given the manner in which it was obtained.
Specific rules exist in sub-section 2 in relation to evidence of admissions where an admission is deemed to have been obtained improperly if any of two things occurred during questioning of a person:
Impropriety includes the conduct described in sub-section 2. Impropriety is further defined in s 139, which relates to police procedures and is of no relevance to civilian law enforcers. It is not open to courts to import whole new concepts into the definition of statutory wording when there is sufficient material to establish a clearly defined range of meanings. Because there is nothing to suggest that courts can stretch the meaning of impropriety to include the moral standards or preconceptions of the presiding judicial officer, it is not anticipated that courts will take any sort of expansive view of what amounts to impropriety.
Nevertheless in Waverley Council v Tovir Investments evidence obtained through undercover surveillance by a private investigator in a residential premises was ruled to have been obtained improperly. An investigator was contracted by Waverley Council to obtain evidence of the use of certain allegedly residential properties were being used as backpackers’ hostels. The method to be used was to pose undercover as a backpacker seeking accommodation while filming the events covertly. The reasons for the ruling included factors that raise suspicion of an attempt by the Council to circumvent existing laws that would prevent them from obtaining the same evidence, but the fact of undercover operations also had some effect. Factors on the side of propriety related mostly to the need to enforce obedience to a court order. It was also considered that any breach of law was inadvertent rather than deliberate....
ORDER FOR FULL TEXT.
 Waverley Council v Tovir Investments Pty Ltd and Rappaport (No 2)  NSWLEC 21.
 McDermott v R (1948) Unreported, HCA, Dixon J, 23 Aug & 22 Sept 1948.
(a) Anything was done or omitted during questioning which the questioner ought to have known was likely to impair the ability of the person being questioned, to respond rationally;
(b) A false statement was made during questioning which the questioner ought to have known was likely to elicit an admission.