The defences of insanity, substantial impairment by abnormality of mind and automatism play a vital role in avoiding criminal liability. Principally, the defences reflect the idea that intellectually challenged individuals should not be penalised but rather treated of their mental impairment. However the outcomes of each defence have also been criticised as ‘anomalous and arbitrary’ due to conflicting legal and medical definitions. Consequently, support for the abolishment of these defences has been proposed to be replaced by sentencing discretion so that consistent and proportionate application of the law is achieved. However ultimately, abolishing the defences is undesirable as it is both ineffective and morally wrong to punish the
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In R v Lloyd ‘substantial’ was held to mean ‘more than a trivial degree but less than total impairment’. The effect of this is that courts are reluctant to allow expert opinion to put forth a ‘quantitative opinion’ as it is incongruous to legal analysis. Like the defence of insanity, a long-winded technical debate attempting to define and diagnose the impairment may ensue. This can unnecessarily complicate the jury’s verdict leading to inefficiency and costly litigation, as demonstrated by Chayna. Hence to maintain the integrity of the defence of SIBAM, legislation prohibits expert opinion validating manslaughter, thereby upholding the jury’s role [s 23A(2)]. A similar reform of the defences of automatism and insanity, ensuring the verdict avoids a heated debate on justifying various diagnoses, will prevent trial from becoming unreasonably complex. McSherry believes that expert evidence needs to be precluded from dappling with the ‘ultimate issue’ of voluntariness, which should be the jury’s role.
Sentencing and Institutionalisation of ‘Dangerous Persons’
Lawbreakers that are mentally impaired should give grounds to either a mitigating sentence punishment or “acquittal” for psychiatric treatment. However punishment is a “communicative element” and it is therefore futile to condemn individuals who fully lack the capacity to control or comprehend the ‘wrongness’ of unlawful acts (not including those suffering from SIBAM). The trend towards