Problems Arising from Broad Definitions of Mental Incapacity Defences Generally, the law acknowledges that mentally incapacitated offenders should not be treated in the same way as offenders of rational intelligence. Insanity is defined by the M’Naghten Rules as a ‘defect of reason’ caused by ‘disease of the mind’. However this classification of insanity has been criticised for being too broad often making it difficult to contrast from automatism. Automatism, described by Lord Goddard as akin to a novus actus interveniens causing involuntarily muscle movement, theoretically differs from insanity in two major instances. It is characterised by: 1.aetiology of an external kind (the ‘internal’/’external’ test) 2.minimal likelihood of recurrence
However in practice, the ‘internal’/’external’ test is a random and subjective attempt to distinguish insanity from automatism. Thus in Quick & Paddison and Hennessy the strikingly similar cases of hyperglycaemia and hypoglycaemia resulted in automatism succeeding only in the former. The sole disparity between the two cases was that in the first, injection of insulin was regarded as an external factor. Failure to take insulin, however, was triggered by an ‘inherent defect or disease’ (hypoglycaemia) so that the defence amounted only to insanity. Yet to put two very similar cases in almost opposite categories is undoubtedly tenuous and greatly subjective.
This weak distinction enables courts to deliberately circumvent the law through the defence of automatism which is apparent through a comparison between the epileptic and dissociative cases of Sullivan and Falconer . In Falconer automatism succeeded on the grounds that the ‘psychological blow’ was an external factor caused by stress. Yet a similar argument failed in the case of Sullivan, even though both dealt with a malfunctioning of the brain. The determining factor was that the epileptic disorder, not stress, had caused the ‘defect of reason’. This vague distinction has been condemned by Schroeder JA, who describes the defence of “psychological blow automatism” as “the last refuge of a scoundrel”. The breadth of interpreting insanity (and automatism) shown by its arbitrary application, therefore prompts a need to reformulate the defence by ‘legislatively delineating’ its scope to ensure appropriate outcomes are applied and to simultaneously eliminate loopholes in the automatism defence.
The risk of loopholes is particularly relevant to medical opinion where the jury is often subject to a ‘battle of experts’ that is especially inconsistent within the legal context of diminished responsibility. S23A of the Crimes Act 1900 defines substantial impairment by abnormality of mind (SIBAM) as an impaired capacity to understand events, to judge wrongness or...