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Diminished Responsibility: A defence to murder

“Diminished responsibility” is a defence to murder. The burden of proof is on the defendant to show that is more likely than not that he suffered from such abnormality of the mind that, having unlawfully killed another person, his conviction ought to be for manslaughter as opposed to murder. The practical effect, in so far as the defendant is concerned, is that the sentencing judge has a discretion on sentence. Sentence following a conviction for murder is a mandatory one of life imprisonment (release only at the discretion of the Home Secretary at a time after the expiry of a minimum period known as a ‘tariff’). Sentence following a conviction for manslaughter is at the discretion of the trial judge up to a maximum of life imprisonment which will depend on the facts of the case. The difference is the defendant’s state of mind. Murder is a crime of specific intent, manslaughter is not. Those who kill because they are mentally ill should be afforded some leniency as they are less responsible for their actions. The defence of ‘diminished responsibility’ applies in such circumstances and is prescribed by section 2 Homicide Act 1957 as amended by section 52 Coroners and Justice Act 2009.

In order to prove he was suffering from diminished responsibility a defendant must show:

  1. He was suffering from an abnormality of mental functioning;
  2. From a recognised medical condition;
  3. Which substantially impaired his ability to understand his conduct, form a rational judgment or exercise self-control;
  4. Which provides an explanation for being party to the killing.

In the recent case of R v Golds [2016] UKSC 61 the Supreme Court was asked to clarify the meaning of the word ‘substantially’ which has been the subject of inconsistent variation over the years. In this case, the defendant stabbed his partner to death in a frenzied knife attack having argued with her on and off for much of the day. Psychiatrists agreed that that there was abnormality of the mind but disagreed as to its cause. The Court held that the meaning of “substantial” was an “impairment of consequence or weight” and not “any impairment which is greater than merely trivial”. In this case, the defendant had failed to discharge the burden of whether or not the impairment was the significant contributory factor of the death and hence the question of whether such impairment was ‘substantial’ was not actually material to the case and the appeal was dismissed.


Thus, for a defendant to succeed in discharging the burden to prove his defence of diminished responsibility he must be suffering from a recognised condition which impairs his mind to such an extent that he is unable to exercise self-control. But it is not enough that he should be suffering from this condition, or have suffered from such a condition, but it must also be the contributory factor that led to the act of the unlawful killing in the mind of the jury. The substantial impairment must be causative.



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Articles are intended as an introduction to the topic and do not constitute legal advice.