For most of the twentieth century, the only oversight of police interrogation practices in the United Kingdom and Australia was a set of nine guidelines known as the 'English Judges' Rules'. These were initially formulated to ensure that police did not obtain defendants' statements in ways that compromised or might later jeopardise the admissibility of confessional material in evidence. The Rules were included in most Australian police operational manuals, but they were 'rules of practice' rather than law. Trial judges held discretionary power to admit a confession even when police breached the Rules. There is little available research on how police applied the Rules before reforms were instigated in the 1980s and 1990s, after inquiries in both the UK and Australia revealed systemic police corruption. This article analyses Queensland police interrogation practices in the mid twentieth century to establish the extent to which detectives observed the Rules. Police testimony from depositions in sixty committal hearings shows that the Judges' Rules were inconsistently applied by Queensland police between 1926 and 1961 and that breaches were more common for some rules than others. There is also evidence of breach practices changing over time, as defendants' guilty pleas accelerated from the late 1940s.