Tonkin v Police

The appellant, Tonkin, appealed against his conviction in the Magistrates Court for driving while under the influence of alcohol, contrary to s 47B of the Road Traffic Act 1961 (SA). The Supreme Court was tasked with determining whether the evidence presented at trial was sufficient to rebut the presumption that the results of a breath analysis instrument accurately recorded the concentration of alcohol in Tonkin's blood, as provided for under s 47G(1) of the Act. The court also considered s 47G(1a) of the Act, which outlines the permissible forms of evidence to rebut the presumption, and the adequacy of the evidence presented by Tonkin to challenge the presumption.

The legal issue at the heart of this appeal was whether the evidence tendered by Tonkin was sufficient to rebut the presumption that the results of the breath analysis instrument accurately recorded the concentration of alcohol in his blood. The court had to consider whether the evidence concerning the alcohol elimination rate was sufficient to establish that the breath analysis instrument gave an exaggerated reading of the concentration of alcohol present in Tonkin's blood. This required the court to determine if Tonkin had discharged the onus of proving, on the balance of probabilities, that the breath analysis reading was "exaggerated" within the meaning of s 47G(1b) of the Act.

The Supreme Court found that the evidence presented by Tonkin was not sufficient to rebut the presumption that the breath analysis instrument accurately recorded the concentration of alcohol in his blood. The court emphasised that to rebut the presumption, Tonkin had to demonstrate that the breath analysis reading was "exaggerated" in the sense that it was outside accepted margins for error, indicating that the instrument did not function properly or was not operated correctly. The court noted that a finding of exaggeration could not be made merely because a blood alcohol test resulted in a lower reading or because the breath analysis reading placed the offence in a more serious penalty category. The evidence presented by Tonkin did not meet this threshold, and thus the presumption under s 47G(1) remained unchallenged.

The appeal was dismissed, and the conviction in the Magistrates Court was upheld. The Supreme Court confirmed that the evidence presented by Tonkin did not establish, on the balance of probabilities, that the breath analysis instrument gave an exaggerated reading of the concentration of alcohol in his blood. Therefore, the presumption under s 47G(1) of the Act that the breath analysis result accurately reflected the concentration of alcohol in Tonkin's blood remained intact.