Mental Health Issues and Criminal Responsibility for Murder: Has Criminal Law Actually Addressed the Impact of Medical Conditions on Criminal Responsibility for Murder

Abstract

The recognition of medical conditions in UK criminal law has evolved, improving examinations of criminal responsibility for murder and upholding justice. Although UK law has made efforts to acknowledge the impact of medical conditions on accountability for murder, limitations in the law’s approach continue to hinder full acknowledgement of the effects. This article will adopt a doctrinal approach to argue that, despite statutory reforms, the law still prioritises moral liability over clinical evidence, which risks inconsistent treatment of defendants with recognised medical conditions. Statutory provisions, case law, and judgments towards convicted defendants with mental health conditions will be utilised to explore the extent to which criminal law in the UK has addressed the defendant’s clinical condition when assessing their liability for murder. The analysis outlines both the law’s advancements and limitations when addressing the impact. Insights into how the law may improve their approach towards assessing the impact will be provided.

Introduction

Criminal law in the UK utilises Sir Edward Coke’s definition of murder, which is the intention to unlawfully kill their human victim outside of war combat, thus under the King’s Peace. Despite the simple definition, not all defendants that unlawfully kill outside of combat are convicted of murder. Cases such as R v Byrne have demonstrated the law’s willingness towards recognising impairments in mental functioning when assessing the defendant’s culpability. However, cases like R v Dowds signify the limits to the law’s willingness, particularly when voluntary conduct is involved. The inconsistency with judicial interpretations raises questions about the legitimacy of defences and partial defences, which imply the law’s inadequate treatment of medical conditions. This article examines whether criminal law in the UK has adequately addressed the impact of medical conditions on accountability for murder. The law’s progress and limitations will be considered.

Research Methodology

The article will utilise a doctrinal approach. This article will examine the effectiveness of legislation. The efficiency of section 2 of the Homicide Act 1957 (HA 1957) after the amendments of section 52 of the Coroners and Justice Act 2009 (CAJA 2009) will be analysed. Case law that utilised section 2 of the HA 1957 will be evaluated to assess successful and unsuccessful applications of diminished responsibility. Another piece of legislation that will be scrutinised is section 54 of the CAJA 2009, while also addressing section 55. Case law will be integrated to examine the applications of loss of control that resulted from a qualifying trigger. Prior defences before statutory reform will be considered whilst examining case law. Secondary sources such as journal articles, academic textbooks, and websites will be incorporated.

Diminished Responsibility under the Homicide Act 1957 (HA 1957)

To address the impact of medical conditions upon culpability for murder, the UK enacted section 2 of the HA 1957 and amended it with section 52 of the CAJA 2009. Section 2 of the HA 1957 outlines that defendants convicted of murder may have their conviction reduced to manslaughter if they were suffering from abnormal mental functioning caused by a recognised medical condition that substantially impaired their ability to understand their conduct; form rational judgments; or exercise self-control. The statutory reform of section 52 of the CAJA 2009 clarified that only recognised medical conditions qualify and highlighted that impairment must be significant. This reform signifies the law’s developing acknowledgement of medical conditions in murder cases. This clarification assisted courts with understanding what embodied a “recognised medical condition” and “substantial impairment.” Thus, it allowed improved evaluations of medical evidence when assessing culpability. This represents development from the common law approach where defendants used to plea under diminished responsibility by claiming their actions were caused by a “disease of mind”. Thus, this reflects the law’s increased acknowledgement that medical conditions can diminish culpability for murder.

The case of Byrne signifies how the enactment of section 2 of the HA 1957 has helped the law acknowledge that medical conditions can make defendants less culpable for murder. In Byrne, medical evidence proved that his abnormal sexual urges impaired his ability to exercise self-control, which constituted abnormal mental functioning caused by a recognised medical condition. Byrne’s abnormal sexual urges constituted a recognised medical condition because his sexual urges were impossible to resist. Hence, Byrne’s murder conviction was reduced to manslaughter. However, the case of Dowds demonstrated the law’s limitations by portraying that, despite acute intoxication being a recognised clinical condition, it was an invalid defence for stabbing someone 60 times because his intoxication was voluntary. Hence, the court presumed that he intended murder regardless of intoxication. Therefore, the court upheld Dowds’ liability for murder to prevent voluntary intoxication from excusing murder. 

Although the law’s recognition of abnormal sexual urges in Byrne highlights the law’s advancement in addressing medical conditions, its dismissal of acute intoxication in Dowds reveals the law’s prioritisation of personal liability over clinical evidence, despite statutory reform. Scholars argue that this reflects unfair judicial choices, because prioritising policy control over fairness fails to adequately address the impact of medical conditions upon responsibility for murder. Thus, it risks the law mistreating defendants with mental impairments and undermines fairness, possibly weakening public confidence in whether the law addresses medical conditions when assessing culpability. The law could enhance consistency by improving the incorporation of medical evidence when addressing culpability.

Partial defence of Loss of Control under the Coroners and Justice Act 2009 (CAJA 2009)

Aside from amending section 2 of the HA 1957, section 54 and section 55 of the CAJA 2009 introduced the partial defence of loss of control. Although loss of control focuses on situational triggers, it is relevant to mental health issues because impairments in self-control, such as those caused by clinical conditions, may diminish liability for murder. The requirements to utilise loss of control as a partial defence under section 54 is that: the defendant’s actions derived from a loss of control that had a qualifying trigger and an objective test of whether a person of the same sex and age with a normal degree of tolerance and self-restraint might have responded similarly. Section 55 defines qualifying triggers as: fear of serious violence and things said or done causing a justifiable sense of being seriously wronged. However, sexual infidelity is excluded under section 55(6)(c). The provisions of section 54 and section 55 replaced the partial defence of provocation under section 3 of the HA 1957, which was criticised as favouring enraged men at the expense of women who killed their abusers. This demonstrates growth as the law is considering psychiatric impairments by recognising that extreme emotional responses, especially from medical conditions, may reduce culpability.

However, case law exposes the law’s limitations in acknowledging evidence of clinical conditions. The objective test under section 54 may fail to account for the impact of medical conditions upon culpability. This was illustrated in R v Goodwin after the court denied that Goodwin beating his victim 18 times with a hammer constituted a loss of self-control because he did not have a qualifying trigger under section 54. Furthermore, the limited qualifying triggers under section 55 may exclude certain cognitive impairments, particularly in defendants with medical conditions. This was portrayed in R v Asmelash, where the court refused to consider the defendant’s alcohol dependency when examining loss of control. Although the court aimed to uphold personal responsibility in both cases, these exclusions risk oversimplifying psychiatric impairments as voluntary wrongdoings, which may influence courts to perceive emotional outbursts as intentional offences. These cases unveil that the statutory reforms still fail to sufficiently address medical conditions that hinder self-control. Consequently, this undermines fairness for defendants with mental health conditions because it ignores how clinical conditions can weaken self-control. Hence, public confidence in the law’s consideration of medical evidence could be diminished. This calls for improved flexibility in considering psychiatric impairments from medically recognised conditions, which would strengthen the law’s understanding of clinical conditions upon culpability.

Another limitation emerges from the elimination of sexual infidelity as a qualifying trigger under section 55(6)(c), which was reaffirmed in R v Clinton after he stabbed his wife because she was having an affair. The court presumed that Clinton’s violence was premediated rather than originating from a loss of control because the court reviewed prior evidence of violence in their relationship. Although the court allowed partial flexibility in Clinton by considering that sexual infidelity can accompany other qualifying triggers, the elimination exposes a conflict between deterring revenge, which upholds moral liability, and considering mental health disorders. Moreover, the exclusion overlooks how sexual infidelity could provoke emotional outbursts in defendants with mental health conditions, disregarding the interaction between psychiatric impairments and medical conditions. Overall, the cases indicate that, despite statutory reform, the partial defence of loss of control remains inadequate in accounting for the impact of psychological conditions in murder cases.

Provocation

Prior to the reforms of the CAJA 2009, the common law partial defence to murder was provocation under section 3 of the HA 1957. Provocation was the unlawful killing committed by a defendant while provoked, leading to a loss of self-control. The requirements for provocation were: the defendant must have acted on a sudden and temporary loss of control immediately after provocation, and their provocation must have been sufficient to cause a reasonable person to act similarly to the defendant. This is examined by an objective test, which would reduce their conviction of murder to manslaughter. However, it eliminated sexual infidelity, revenge, and premeditation, which restricted the defence’s scope, thus reducing its capacity to address the impact of the excluded triggers on mental health conditions. 

The application of provocation exposed more limitations in acknowledging clinical conditions that impact mental health. In R v Ahluwalia, the defendant set her husband alight after enduring 10 years of domestic abuse. The court struggled to accommodate Ahluwalia’s gradual loss of control because the loss of control must be an instantaneous reaction after provocation, which the court affirmed in R v Duffy after she beat her abusive husband to death. Although the court did exercise limited flexibility in Ahluwalia by considering cumulative abuse, it illustrates how the law’s rigid interpretation failed to recognise that clinical conditions do not always lead to an immediate loss of control following provocation. Furthermore, critics argued that these cases were proof that provocation ignored abused women, demonstrating that the law failed to account for emotional trauma caused by clinical conditions that developed after prolonged abuse. Similarly, in R v Dietschmann, the defendant killed a man while he was intoxicated and grieving his aunt’s death. Thus, the court had to assess the interaction between the provoking event and diminished responsibility based on his grief. 

The inconsistencies in these cases highlight that, under provocation, the law historically struggled to integrate medical evidence of mental health disorders into examinations of liability for murder. Although provocation recognised certain triggers, the law’s strict application presumed that gradual responses to provocation were premediated rather than an abrupt loss of control. This limited the courts’ recognition of medical conditions that influence self-control. These issues mimic the current obstacles under the judicial interpretations of the HA 1957 and the CAJA 2009. Considering the case law, the historical approach under provocation displays that, prior to statutory reform, the law inadequately addressed the interaction between mental health issues and liability for murder. This reinforces that, historically and currently, the law struggles with addressing medical conditions in a way that is fair for defendants with clinical conditions.

Recent Developments

• On June 13, 2023, in R v Calocane, Valdo Calocane killed three people in Nottingham. He was diagnosed with paranoid schizophrenia, which allowed him to plea under diminished responsibility, thus reducing his conviction of murder to manslaughter. He was detained to a high-security hospital under section 37 and section 41 the Mental Health Act 1983. This caused public outrage and debates over whether the law became too lenient in accepting diminished responsibility as a defence by eluding responsibility for murder.

• Following Calocane, Her Majesty’s Inspectorate of Constabulary and Fire & Rescue Services (HMCPSI) urged the UK government on 2 September, 2025, to consider different tiers for classifying homicide to improve public confidence and deliver justice for the victims’ families. However, the UK government is currently not considering a three-tier classification for murder, such as first-degree and second-degree murder.
• The CPS “Mental Health: Suspects and Defendants” guidance was updated on 11 May 2023 and 15 October 2024 to flag mental health conditions at all stages of a criminal case so that it is considered during charging, fitness to plead, and sentencing.

Suggestions for a Way Forward

The courts should improve the balance between considering voluntary acts with the behavioural effects of recognised clinical conditions. Additionally, stronger utilisation of psychiatric evidence and precise legislative guidance would improve consistency in cases that utilise diminished responsibility and loss of control as defences. Hence, it would make defence and partial defence cases fairer.

1. Develop statutory guidance under the HA 1957 and CAJA 2009 to inform how courts should handle voluntary actions against cognitive impairments caused by mental health disorders.
2. Expand the scope of medical conditions by addressing the impact of prolonged cognitive impairments when examining diminished responsibility or loss of self-control.
3. Provide training for Judges, the defence team, and prosecutors to enhance judicial understanding of the interaction between mental health conditions and accountability for murder.
4. Ensure that the CPS “Mental Health: Suspects and Defendants” guidance is applied consistently during charging, fitness to plead, and sentencing.

Conclusion

The statutory reforms to section 2 of the HA 1957 under section 52 of the CAJA 2009 have demonstrated that UK criminal law has progressed in addressing the impact of medical conditions on criminal responsibility for murder. This is evident compared to the previous common law partial defence of provocation, which was criticised for its inadequacy. However, courts continue to prioritise moral liability over clinical evidence of psychiatric impairments in murder cases concerning voluntary actions. Furthermore, restrictive qualifying triggers under section 55 of the CAJA 2009 have influenced courts to overlook the debilitating effects of cognitive impairments on self-control. Although improvements to the CPS guidance and proposed reforms following Calocane suggest evolving awareness of mental health conditions on culpability, statutory and procedural reforms remain necessary to increase fairness and consistency in murder trials. This would enhance public confidence in the law’s approach to addressing the impact of mental health conditions on culpability. Considering the inconsistencies in case law, expanding the scope of recognised clinical conditions could improve how the law handles cases involving voluntary actions and clinical evidence of cognitive dysfunction. This would ensure that defendants with clinical conditions are charged appropriately. Thus, it would strengthen how criminal law addresses the impact of mental health issues on liability for murder.

Bibliography

Statute:

• Coroners and Justice Act 2009
• Homicide Act 1957
• Mental Health Act 1983

Case law:

• R v Ahluwalia [1992] 4 All ER 889.
• R v Asmelash [2013] EWCA Crim 157, [2014] QB 103.
• R v Byrne [1960] 2 QB 396.
• R v Calocane [2024] EWCA Crim 490, [2024] 4 All ER 1063.
• R v Clinton [2012] EWCA Crim 2, [2012] Crim LR 539.
• R v Dietschmann [2003] UKHL 10, [2003] 1 AC 1209.
• R v Dowds [2012] EWCA Crim 281, [2012] 1 WLR 2576.
• R v Duffy [1949] 1 All ER 932.
• R v Goodwin [2018] EWCA Crim 2287, [2018] 4 WLR 165.

Books:

• Thomas M, Criminal Law (3rd edn, HALL & STOTT PUBLISHING 2023).

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• Baker J, Edwards I and Beazley P, ‘Juror decision-making regarding a defendant diagnosed with borderline personality disorder’ (2021) Psychiatry and Law 1.
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• Medland S and Nathan R, ‘Psychiatric expert evidence and the new partial defence of diminished responsibility and loss of control’ (2018) 22 (4) BJPsych Advance 277.
• Menon M NR, ‘R v Ahluwalia: The Vindication of Battered Women’ (1993) 5 (1) National Law School Journal 172.
• Slavkovic V, ‘The Doctrine of Provocation and a Murder Based on Jealousy (2023) 127 Vilnius University Press 159.
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• Wu A, ‘Going Full Circle: Gender and the ‘Loss of Control’ Defence under the Coroners and Justice Act 2009’ (2019) 1 Rule of Law Journal 46.

Websites:

• CPS.Gov.UK, ‘Mental Health: Suspects and Defendants’ (14 October 2019) <https://www.cps.gov.uk/legal-guidance/mental-health-suspects-and-defendants> accessed 11 September 2025.
• HMCPSI.justiceinspectorates.Gov.UK, ‘Government urged to change homicide laws, says HMCPSI’ (2 September 2025) <https://hmcpsi.justiceinspectorates.gov.uk/news/government-urged-to-change-homicide-laws-says-hmcpsi/> accessed 11 September 2025.
• Mountfordchambers.com, ‘Murder – a case for reform.’ (24 April 2024) <https://www.mountfordchambers.com/murder-a-case-for-reform/> accessed 11 September 2025.