Sharon O'Brien, R (on the application of) v HM Assistant Coroner for Sefton, Knowsley and St Helens

Coronial causation requires proof on the balance of probabilities that the relevant event or conduct made an actual and material contribution to death, more than minimally, negligibly or trivially. The question is probability, not certainty. Judicial review of a coroner’s scope decision concerns whether the decision was premature or irrational; the reviewing court must not substitute its own factual assessment. A coroner should consider readily obtainable material relevant to the counterfactual, including criminal antecedents and the likely consequences of charging, bail and sentencing. In domestic-abuse cases, apparent tolerance of an abuser does not eliminate the risk. Expert evidence about likely criminal-process outcomes may be admissible where it supplies knowledge outside the court’s experience.

Linda O’Brien died after falling from a flat window while Alan McMahon was present. The coroner decided that the inquest should focus on the events immediately surrounding the death, that no jury was required, and that Article 2 was not engaged. He concluded that police acts or omissions on 7 April 2020 had not causally contributed to the death on 9 May 2020.

Sharon O’Brien sought judicial review of the restriction on scope. Permission was granted only on the ground that the coroner had prematurely and irrationally decided the causation issue. The High Court dismissed the claim, finding that it could not be shown on the balance of probabilities that an earlier arrest would have resulted in McMahon being in custody on the date of death. The central issue on appeal was whether that approach unlawfully substituted the High Court’s factual assessment for review of the coroner’s decision.

1. Disposition. The appeal was allowed. The coroner’s decision was quashed and the matter remitted to another coroner. The decisions concerning the need for a jury and whether Article 2 was engaged also required reconsideration because they rested on the premature causation decision.
2. Judicial review. The High Court had erred by making its own findings about what would have followed an arrest. Its task was to review whether the coroner had acted prematurely or irrationally. A coroner has a wide discretion to set the bounds of an inquest and determine the evidence, but that discretion must be exercised on a lawful and rational evidential basis. The possible cost or complexity of an investigation did not justify excluding police conduct relevant to causation.
3. Causation. The governing test, explained in R (Tainton) v HM Coroner [2016] EWHC 1396 (Admin), was proof on the balance of probabilities that the relevant conduct contributed to death more than minimally, negligibly or trivially. The requirement of an actual and material contribution did not impose a higher standard of certainty. The question for the inquest was whether arrest on 7 April 2020 would probably have prevented the death on 9 May 2020.
4. Counterfactual criminal process. The criminal justice process could be assessed probabilistically. The court should assume that police, prosecutors and sentencing courts would act rationally on the evidence and applicable guidance. The absence of McMahon’s antecedents and the failure to consider the relevant charging, bail and sentencing consequences made the coroner’s conclusion premature and irrational. The evidence suggested that an immediate custodial outcome was highly likely.
5. Expert evidence and jury threshold. The principle in R v Turner [1975] QB 834 was not confined to scientific evidence. Expert opinion may be admitted where it supplies information outside the court’s experience, although it is unnecessary where the court can reach its own conclusion. The judge was wrong to impose a blanket ban on expert evidence. Under section 7(2)(b) of the Coroners and Justice Act 2009, the threshold for a jury is merely a reason to suspect that death resulted from a police act or omission. The evidence provided a proper basis for that investigation, without finally determining causation.

• Court of Appeal (Civil Division): Appeal allowed. The coroner’s decision was quashed and the matter remitted to another coroner for reconsideration, including the jury and Article 2 issues. [2026] EWCA Civ 499
• High Court: His Honour Judge Sephton KC, sitting as a Judge of the High Court, dismissed the judicial review claim and held that the coroner’s decision was neither premature nor irrational.