A police officer's opinion that a potential prosecution witness is unreliable and untruthful is inadmissible opinion evidence under ss 76-79 of the Evidence Act 2008 (Vic), and also inadmissible as credibility evidence under ss 101A and 102. However, the wrongful admission of such evidence will not occasion a substantial miscarriage of justice where the jury's verdict plainly flowed from acceptance of the complainant's evidence and the impugned evidence merely went to the creditworthiness of an uncalled witness. Where the defence case is that no sexual activity occurred, the failure to call a witness whose evidence consistently supported the occurrence of sexual activity cannot occasion a miscarriage of justice, as the uncalled witness's evidence would have supported the prosecution case on the central issue.
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