Diminished responsibility

Partial defences to murder were originally introduced to avoid the death penalty. Today they remain in use to avoid a mandatory life sentence and indeed the obvious stigma attached to a murder conviction. Focusing in particular on diminished responsibility, and what is defined as ‘a substantial impairment of mental ability’.


The question advances that the meaning of substantial and recent interpretation is now too narrow following the Supreme court decision in R v golds (Golds). In criminal law, diminished responsibility (DR) is a potential defence by excuse where defendants argue that although they broke the law, they should not be held fully liable because their mental functions were impaired. The defence of diminished responsibility was reformulated. Consequently, a special defence can apply only to murder under s.2(1) of the Homicide Act 1957 which was amended by the s.52 Coroners and Justice Act 2009 .Three requirements have to be met, where a person who kills is not to be convicted of murder and if defendant was suffering from an abnormality of mental functioning.


The first requirement is that defendant must have suffered from an abnormality of mental functioning. In R v Byrne. it was held that the defendant’s state of mind was significantly different from that of an ordinary human being that a reasonable man would term in abnormality. This would lower the conviction to voluntary manslaughter, and he would avoid the mandatory life sentence. The second requirement is that abnormality must come from a recognised medical condition

. This can be anything that the World Health Organisations list of illnesses including depression, pre-menstrual syndrome and PTSD . In R v. Dowds the Court of Appeal mentioned that just because a disease is listed it does not necessarily mean it will be a recognised for the purpose of DR. It would have to be proved by medical evidence, possibly from expert witnesses. However, the jury will aim to examine whether the abnormality is the reason behind the defendant’s conduct. In the case of R v. Anthony Martin, the legal principle of defence of DR can be applied where D has a paranoid personality disorder and depression.


The third part requires substantial impairment of the defendant’s ability to form rational judgements, understand the nature of his conduct or exercise self-control.

R v Lloyd  states that substantial impairment means more than minimal but less than the total impairment, if established on balance of probabilities the verdict must be manslaughter.

The sentence will almost certainly be much more lenient than the mandatory life-sentence for murder. The latest authority was in the case Golds where it decided that the definition of substantial was incorrect. The right approach is when the jury members to ask of a definition, they should be instructed that substantial means significant therefore it is more than trivial.


Significant contributory factor to the killing is the new addition to the defence of diminished responsibility, under s.2(1) (b) a clarification was made that the cause or significant cause in D killing the victim, if it made no difference where he/she would kill anyway the defence will not be available. In R v. Osborne, The Court of Appeal rejected the appeal, it would have been accepted if ADHD was the support of DR defence however, it did not substantially impair his mental responsibility, but the use of drugs and anger explained his conduct. In R v. Hobson, the court accepted that ‘battered woman’s syndrome’ was a mental disease and could cause abnormality of the mind. Furthermore, the new definition is likely to be interpreted more narrowly because it creates unfairness between the cases which leads to inconsistency as the jury are emotionally attached and have no legal background which suggests that they view the case in an objective manner rather than an expert point of view. It can lead to unfortunate punishments due to unfair judgements from the jury. It gives the jury a restriction as there is no guarantee they could interpret substantially impaired too harsh or too generous. However, when the jury’s definition of substantial is not in line with the legal definition, the judge will remind the jury of the statutory definition to ensure the case is fair.


In conclusion, having the defence of diminished responsibility is convicted of manslaughter and is often imprisoned. The modern rationalisation leads to the unfair judgments by the jury leading to the judge being unable to be flexible when sentencing, as the jury may be too harsh with their definition of substantial impairment. However, if the defence of DR is abolished, a mentally disabled defendant might not be able to plea the defence because of its narrowness and therefore he will be convicted of murder.


Lawyer: Maram Al Lawati

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