The High Court has unanimously allowed an appeal from a decision of the Full Court of the Supreme Court of South Australia on judicial discretion to exclude evidence that was unfairly or improperly obtained. Dunstall was stopped by police while driving and failed a breathalyser test. A subsequent blood test, to which a person is entitled under s 47K(2a) of the Road Traffic Act 1961 (SA), was incorrectly administered at a nearby hospital, and the two samples it produced were unsuitable for later analysis and hence could not be used to challenge the breathalyser reading. Both a single judge of the SASC and a majority of the Full Court (Kourakis CJ dissenting) upheld the Magistrate’s decision to exercise judicial discretion to exclude the evidence of the breathalyser reading on the basis that Dunstall could not obtain a fair trial because he had lost the opportunity to challenge it. Gray J held that the statutory safeguards were ‘rendered nugatory’ because of the failed test (at [78]) and Dunstall was placed in the same position as if he had not been informed of his rights or provided with a test kit (as the statute requires): at [79], [87]. Sulan J held that Dunstall had done all that could be reasonably expected of him and, through no fault of his own, was deprived of the proper right to challenge the breathalyser analysis ([170] and [168]).

The Court held that the magistrate erred in exercising the discretion to exclude the evidence of the breathalyser reading. The joint judgment (French CJ, Kiefel, Bell, Gageler and Keane JJ) held that the respondent’s arguments about the applicability of the ‘general unfairness discretion’ — which allows a court to exclude probative evidence that was neither improperly obtained nor carried a risk of prejudice if the reception of that evidence would make a trial unfair (see [23]), and which could extend to instances where the weight and credibility of the evidence could not be effectively tested (see at [31]ff) — failed ‘to come to terms with the legislative scheme’: ‘The Parliament has chosen to provide the prosecution with an aid to proof [in the breath analysis reading] and to closely confine the circumstances in which rebuttal evidence may be adduced’: [36]. That scheme does not give a defendant a statutory right to a blood test taken in accordance with proper procedures: ‘The onus is on the defendant to bring himself or herself within [the confines of s 47K(1a)]. It is evidence that a defendant may fail to do so in a variety of circumstances without personal fault’: [43]. Because admitting the breathalyser reading would not have made the original trial unfair, and because neither party before the High Court contested the existence of the ‘general unfairness discretion’, the joint judgment held that it was inappropriate to determined the scope of any residual discretion (see at [47]), and remitted the matter for a further hearing before the Magistrates Court. Nettle J agreed that the appeal should be allowed, holding that the admission of the breath analysis certificate would not produce an unacceptable risk of miscarriage of justice and therefore could not be excluded on the basis of the fairness discretion ([84], see also at [76]–[83]).