The High Court has clarified that when determining appeals against conviction, there is a materiality threshold which must be met before an appeal will be allowed based on an error or irregularity in a criminal trial. A non-fundamental error or irregularity in proceedings will constitute a miscarriage of justice if the error could realistically have affected the reasoning of the jury.
Note: this decision should be read in conjunction with the High Court decision of MDP v The King [2025] HCA 24, which confirmed that the materiality threshold also applies to wrong decisions on questions of law made by a trial judge. We have reviewed this in 'Materiality matters: High Court clarifies threshold for legal error in criminal appeals'
Matthew Cucu Brawn was tried by jury in the District Court of South Australia and convicted of maintaining an unlawful sexual relationship with a child under the age of 17 years (refer to endnote 1) – namely, a girl between the ages of 5 and 8.
The primary issue was whether the perpetrator was Mr Brawn or another adult in the community.
The complainant initially described being sexually abused by her ‘uncle’. Like many other children in the Sudanese community, the complainant used the term ‘uncle’ to refer to adult male community members. Mr Brawn argued the complainant was untruthful or mistaken in identifying the perpetrator, who could be any other ‘uncle’ in the community.
After Mr Brawn was sentenced, counsel for the prosecution disclosed to his legal representatives that another ‘uncle’ of the complainant, Mr Brawn’s father (‘X’), had previously been charged with sexual offences against another child, his biological niece, during a period overlapping with Mr Brawn’s indictment period.
Mr Brawn appealed to the Court of Appeal of the Supreme Court of South Australia on grounds that the prosecution’s failure to disclose breached their duty of disclosure and resulted in a miscarriage of justice pursuant to ss 158(1) and (2) of the Criminal Procedure Act 1921 (SA) (also known as the common form criminal appeal provision which corresponds to s 6(1) of the Criminal Appeal Act 1912 (NSW)).
The Court of Appeal found the prosecution had breached their duty of disclosure. However, the failure to disclose did not materially amount to a miscarriage of justice as Mr Brawn failed to demonstrate that if the non-disclosed material had been provided, the defence ‘would’ or ‘might’ have been conducted differently.
Mr Brawn appealed to the High Court on the grounds that the Court of Appeal had erred in their finding that the breach of the duty of disclosure did not amount to a miscarriage of justice.
In a unanimous decision, the High Court found that the failure to disclose information about the charges against X amounted to a material error or irregularity in the prosecution and constituted a miscarriage of justice. The threshold for materiality is whether or not the error or irregularity could realistically have affected the reasoning of the jury. ‘Could’ is defined as ‘having the capacity to’, and ‘realistically’ is meant to distinguish from fanciful or improbable possibilities.
Meeting this threshold is not onerous. It does not invite analysis of whether or not, but for the error, the outcome may have been different. In Mr Brawn’s case, the trial defence may not have been conducted differently if the material was disclosed. However, the non-disclosure denied Mr Brawn that opportunity, which could have realistically impacted the jury’s reasoning. The appeal was allowed, and a new trial was ordered.
The High Court’s decision reinforces the importance of timely and complete disclosure, even where the admissibility or value of the material is uncertain. All irregularities or errors in trial conduct (including non-disclosure) that realistically could impact the jury’s reasoning may give rise to a miscarriage of justice.
The clarified materiality threshold is more expansive than the Court of Appeal’s construction, increasing the risk of re-trial where prosecutors fail to fully discharge their disclosure obligations at trial.
1. Criminal Law Consolidation Act 1935 (SA), s 50(1).
Claudia Pendlebury, Director
claudia.pendlebury@cso.nsw.gov.au
Petra Lejins, Solicitor
petra.lejins@cso.nsw.gov.au
The CSO's Regulatory & Environment practice group specialises in advising and representing agencies in relation to regulatory compliance and prosecutions, statutory interpretation advice in the environment and natural resources context, as well as criminal law, evidence and procedure.
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