Diminished responsibility

A special defence to a murder charge.

In the case of voluntary manslaughter the special defences of diminished responsibility along with loss of control, formerly provocation and suicide pact can be said to partially excuse the defendants actions and reduce a charge of murder to manslaughter. Before the Homicide Act 1957 the defence of diminished responsibility did not exist, the only defence available to a person with mental problems would have been insanity.

If the necessary mens rea has been proved and the defendant has caused the death of the victim, it may be possible to use the defence of diminished responsibility, loss of control (provocation), suicide pact or infanticide to avoid a conviction for murder. This type of defence is known as a partial defence and can only be used on a charge of murder. If he is successful with this defence the defendant will be sentenced at the discretion of the judge and his liability will be reduced from murder to manslaughter. Because the necessary mens rea has been proved and evidence has been provided to show that the defendant had intended to kill or cause GBH the manslaughter is referred to as voluntary manslaughter rather than involuntary manslaughter which is the unlawful killing of a human being without malice aforethought.

Section 52 of The Coroners and Justice Act 2009 replaces the definition of diminished responsibility in section 2(1) of the Homicide Act 1957. The aim of the reform is to ensure that the defence should not be successful if the defendant would have killed regardless of his mental condition.

 Section 52 states:
“(1) A person (“D”) 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:
(a) to understand the nature of D’s conduct;
(b) to form a rational judgment;
(c) to exercise self-control.

(1B) For the purposes of subsection (1)(c), an abnormality of mental functioning provides an explanation for D’s conduct if it causes, or is a significant contributory factor in causing, D to carry out that conduct.”

  • The meaning of an abnormality of mental functioning is to describe it as being so different from that of an ordinary man that the reasonable man will regard it as abnormal. R v Byrne (1960) CA. The defendant was a sexual psychopath who strangled a woman.  Medical evidence showed that he was not able to control his degenerate behaviour. He was convicted of murder but the conviction was quashed on Appeal and the Court of Appeal substituted a conviction for manslaughter.
  • Arising from a “recognised medical condition”.  Medical evidence must be presented to the jury for them to decide whether the abnormality of mental functioning arose from a recognised medical condition.This covers a wide range of conditions including depressive illness, paranoia,epilepsy and diabetes.

According to the explanatory notes associated with the Act  'The new definition requires that the abnormality substantially impaired the defendant’s ability to do one (or more) of three things and also provides that the defendant’s abnormality of mental functioning should be at least a significant contributory factor in causing the defendant’s acts or omissions.'

Intoxication complicates the defence of diminished responsibility. Intoxication on its own can not be used as a defence of diminished responsibility, the law states quite clearly that the abnormality of mental functioning must be due to a recognised medical condition. It is more difficult when the defendant has some abnormality of mental functioning but is also intoxicated at the time the crime is committed Dietschmann, R (2003).  The House of Lords held that the jury should not find the defendant guilty of murder if they were satisfied that, even though he was intoxicated, he was not responsible for his actions because his 'abnormality of mind substantially impaired his mental responsibility for his acts in doing the killing'. The defendant should be guilty of manslaughter and not murder. Subsequently in Hendy, R v (2006), although he was intoxicated, the defendant had underlying brain damage and a psychopathic disorder and his conviction for murder was changed to a conviction for manslaughter. Similarly in Robson, R v. (2006) the defendant was intoxicated but was shown to have an acute stress disorder and his conviction for murder was changed to a conviction for manslaughter.

The issue of intoxication due to alcohol dependancy was considered in Stewart (2009) and the Court of Appeal set out a three-stage test for juries to consider in such cases:

1. Was D suffering from an ‘abnormality of mind’(now mental functioning)? They pointed out that the mere fact that D has ADS (Alcohol Dependency Syndrome) would not automatically amount to an abnormality. The nature and the extent of the ADS had to be considered.

2. If so, was D’s abnormality caused by the ADS?

3. If so, was D’s mental responsibility substantially impaired? To decide this all the evidence, including the medical evidence ,should be considered. This would involve such matters as the extent and seriousness of D’s dependency and the extent to which he could control his drinking.


BBC News - Kaiya Blake suffocated by mother Chantelle

Acute voluntary intoxication and the amended section 2 Homicide Act 1957

Changes to the law of homicide | News | Law Society Gazette

Homicide; Murder and Manslaughter: Legal Guidance: The Crown

Man convicted and sentenced for manslaughter - Maidenhead

Marine Alexander Blackman conviction reduced to manslaughter - BBC



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