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Criminal | Offences Against The Person

Voluntary Manslaughter: Diminished Responsibility

Revision Note | A Level

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  • voluntary manslaughter is a category of unlawful homicide
  • D who would otherwise be guilty of murder but can plead one of two specific partial defences
  • partial defences: diminished responsibility and loss of control Coroners and Justice Act 2009 (CJA 2009)
  • if D successfully pleads partial defence he may be found guilty of manslaughter
  • manslaughter verdict allows more discretion in sentencing


  • diminished responsibility originally introduced by the Homicide Act 1957 (HA 1957)

    Homicide Act 1957

    • S2(1): ..Where a person kills or is a party to the killing of another, he shall not be convicted of murder if he was suffering from such abnormality of mind (whether arising from a condition of arrested or retarded development of mind or any inherent causes or induced by disease or injury) as substantially impaired his mental responsibility for his acts and omissions in doing or being a party to the killing...
  • extended narrow defence of insanity, to allow a partial defence for Ds suffering from wider range of mental health issues
  • S52 of CJA 2009 amends HA 1957 S2(1)

    Coroners and Justice Act 2009

    • S52(1): A person who kills or is a party to the killing of another is not to be convicted of murder if D was suffering from an abnormality of mental functioning which -
      (a) arose from a recognised medical condition,
      (b) substantially impaired D's ability to do one or more of the things mentioned in subsection (1A)
      (c) provides an explanation for D's acts and omissions in doing or being a party to the killing.
      (1A) Those things are -
      (1A)(a) to understand the nature of D's conduct;
      (1A)(b) to form a rational judgment;
      (1A)(c) to exercise self-control.

Abnormality of mental functioning

  • abnormality of mental functioning replaces old term abnormality of mind
  • case law developed meaning abnormality of mind

    Byrne (1960)

    • D, sexual psychopath, strangled and mutilated V, young female
    • Court of Appeal substituted murder conviction for manslaughter, on basis of diminished responsibility
    • Lord Parker defined abnormality of mind : .. a state of mind so different from that of ordinary human beings that the reasonable man would term it abnormal.. wide enough to cover the mind's activities in all its aspects...
  • likely courts continue to apply same standard of abnormality
  • test is whether D’s mental functioning was so different from that of ordinary human beings that the reasonable man would term it abnormal
  • Recognised medical condition

    • recognised medical condition broad, covers physical and psychological conditions
    • case law found range recognised medical conditions for purpose of diminished responsibility

      English (1981)

      • D killed V, D was suffering from pre-menstrual tension (PMT)
      • D guilty of manslaughter, PMT a recognised medical condition

      Reynolds (1998)

      • D killed V, her mother, with a hammer, D suffering from post natal depression
      • D guilty of manslaughter, post natal depression a recognised medical condition

      Ahluwalia (1992)

      • D killed V, her husband when he fell asleep, D suffering from Battered Woman’s Syndrome
      • D guilty of manslaughter, Battered Woman’s Syndrome a recognised medical condition
    • must be medical evidence to confirm an abnormality of mental functioning caused by the recognised medical condition

    Substantially impaired

    • D’s abnormality of mental functioning must substantially impair his mental responsibility for his conduct
    • term is unchanged from HA 1957, so old case law is relevant

      Lloyd (1967)

      • D strangled V, his wife, D was suffering from depression
      • Court of Appeal considered the meaning of substantial, held it does not mean total nor minimal, and for the jury to decide whether D’s mental responsibility is substantially impaired
      • as it is a question of fact a judge may withdraw the point from a jury if there is no evidence on which a reasonable jury could make such a conclusion
    • substantial impairment must be in relation to one of three aspects of D’s mental responsibility: understanding the nature of his conduct, forming a rational judgement or exercising self control

    Understand the nature of his conduct

    • where D is acting automatically and not aware of his conduct
    • can include people suffering delusions or with severe learning difficulties

    Form a rational judgment

    • if D does know the nature of his conduct but cannot form a rational judgement about his acts or omissions
    • Ds suffering from paranoia or schizophrenia may not be able to form rational judgements

      Martin [2002]

      • D shot intruders at his home, one died and the other was seriously injured
      • D proved to be suffering from longstanding paranoid personality disorder, a recognised medical condition, which substantially impaired his ability to form rational judgement
      • D’s conviction changed to manslaughter on basis of diminished responsibility

    Exercise self-control

    • if D has a recognised medical condition which prevents him from exercising self control

      Byrne (1960)

      • D, sexual psychopath, strangled and mutilated V, young female
      • Court of Appeal substituted murder conviction for manslaughter, on basis of diminished responsibility

    Provides an explanation

    • must be proved that the substantial impairment to the D’s mental responsibility provides an explanation for his conduct
    • causal connection was introduced in CJA 2009
    • abnormality of mental functioning does not need to be the only factor which caused D to act as he did but must be a substantial one


    • diminished responsibility becomes more complex if D was intoxicated at time of the killing
    • general rule: intoxication cannot support a defence of diminished responsibility

      Di Duca (1959)

      • Court of Appeal held immediate effects of alcohol or drugs were not sufficient to amount to an injury (medical condition)
      • there may be an effect on the brain, it was transient and was not an abnormality of mind
    • wording of CJA 2009 strengthens this view, as abnormality of mental functioning needs to be caused by recognised medical condition
    • limiting jury discretion to find diminished responsibility
    • further complications where D suffers some abnormality of mental functioning and is also intoxicated
    • if D satisfies the jury that his abnormality of mental functioning, substantially impaired his mental reasoning at the time of the killing, then they should find him guilty of manslaughter not murder

      Dietschmann (2003)

      • D violently kicked and punched V to death
      • D accused V of damaging a watch given to him by his deceased aunt
      • evidence showed D was suffering from a severe depression caused by grief, D had also been drinking heavily
      • Lord Hutton: .. the important question is: did that abnormality substantially impair his mental responsibility for his acts in doing the killing?..
    • fact D is intoxicated may be irrelevant

      Hendy (2006)

      • D stabbed and killed V, a complete stranger
      • evidence proved D was intoxicated and he had brain damage and a psychopathic disorder
      • Court of Appeal overturned murder conviction and substituted for manslaughter

      Robson (2006)

      • D was heavily intoxicated, suffering from an acute stress disorder at the time of the killing
      • Court of Appeal quashed conviction for murder in favour of manslaughter
    • case law is likely to be followed under CJA 2009
    • further consideration is needed if D is suffering from drug or alcohol addiction and dependency
    • Alcohol Dependence Syndrome (ADS) is a recognised medical condition, a sufferer cannot control their drinking
    • a key factor is whether D exercised control over their intoxication

      Tandy (1989)

      • D strangled V, her 11 yr old daughter, D was an alcoholic who had drunk nearly a whole bottle of vodka before the killing
      • D’s conviction for murder was upheld, evidence showed D exercised control over her drinking that day
      • Lord Watkins: If the alcoholism has reached the level at which her brain had been injured by the repeated insult from intoxicants so that there was gross impairment of her judgment and emotional responses, then the defence of diminished responsibility was available to her ... if her drinking was involuntary, then her abnormality of the mind at the time of the act of strangulation was induced by her condition of alcoholism...
    • approach criticised as it does not consider whether alcoholism is a disease
    • questions over voluntariness and whether D’s alcohol dependency has caused brain damage are important, especially in jury directions

      Wood (2008)

      • D killed the V in a frenzied attack using a meat cleaver
      • experts agreed D defendant had ADS but disagreed whether this damaged his brain
      • jury directed diminished responsibility only available if they found D suffered brain damage or if D’s drinking was involuntary, D convicted of murder
      • Court of Appeal quashed conviction, D’s drinking had to be entirely involuntary

      Stewart (2009)

      • D admitted killing V after an argument
      • D suffered from ADS, argued this made his drinking involuntary and caused brain damage, D convicted of murder
      • Court of Appeal overturned the conviction on the basis of a misleading jury instruction, suggested questions for juries to consider
    • case law relates to HA 1957 similar approach likely under CJA 2009
    • a jury must consider whether D was suffering from an abnormality of mental functioning
    • if so, was this caused by ADS?
    • if so, did this mean D’s mental responsibility was substantially impaired?
    • jury must decide whether the abnormality caused or was a significant factor in causing D to kill V
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