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How just is the defence of insanity?

How just is the defence of insanity?

Anisa Rahman Choudhury


Reading time: three minutes

In the UK, the defence of insanity has been under scrutiny practically from its conception. It’s a special verdict of ‘not guilty’. If the defence of insanity is used, the sentencing judge may decide on absolute discharge, a supervision order or a full hospital detention. While these are intended to not be punishment, defendants can be averse to this defence for the dramatic consequences. This blog will break down the defence and assess whether it needs reform. 

The components of the defence of insanity are most controversial, necessitating that the defendant must’ve been defect of reason from disease of the mind, as not to know the nature and quality of the act he was doing, or if he did know it, that he did not know that what he was doing was wrong” (M’Naghten, 1843). Firstly, therefore, a successful pleading arises only when the defendant can show they were unaware that what they were doing is legally wrong; the illegality test is advantageous in preventing “vague meaning which may vary according to the opinion of different persons”, moral subjectivity of ‘wrongness’ clearly undermining legal certainty. However, even if an individual is unaware of their actions in a technical, moral or political sense, they don’t qualify, which is exemplified in the 2007 Johnson case. While the defendant knew that stabbing the victim was unlawful, he was suffering from delusions so was arguably not aware of his actions in terms of reality. In Finbarr McAuley’s Insanity, Psychiatry and Criminal Responsibility (1993), he rightly proposes that a broader scope is needed to include the defendant’s own realisation of rational justification. 

Secondly, there must be a causal link to the ‘disease of the mind’, which is the key difference between the insanity defence and automatism, the latter requiring an external factor.  Problematically, Lord Diplock states that ‘mind’ in the M’Naghten rules has the ordinary meaning of “mental faculties”; rather than using a medical term to deliberate the cause of unawareness, the insanity defence should be used if the defendant is suffering from a disease that’s affected mental functioning, regardless of the overly broad principle.

Critics of the insanity defence may go a step further: that the distinction between automatism and the insanity defence has created an illogical division. In R v Quick, the defendant, a nurse, attacks his patient while experiencing a hypoglycaemia episode, which was caused by taking insulin on an empty stomach as well as stress. Conversely, the defendant in Hennessy stole a car after he’d had a hyperglycaemic attack from failure to take insulin. Hennessy is distinguished from Quick because the defendant’s state was caused by diabetes rather than something external, like insulin. These outcomes are, however, reasonable. If the defendant in Hennessy was allowed a full acquittal then there would be no basis nor assurance that hyperglycaemic attacks wouldn’t happen again, which are much more severe than hypoglycaemia attacks as well as the potential consequences. In this example, a supervisory order would be more appropriate. Further, the premise of automatism is lack of control but the defendant in Hennessy they’d chosen not to take insulin. 

In Quick, there was also a greater focus in the prospect of curing the disease when deciding the sentence, a more catered and constructive response. Lawton LJ contended that there ought to be reluctance before giving a defence of insanity, seeing whether it can be treated even with acquittal. Thus, there may not need to be such disliking towards the defence of insanity should the courts continue to only give it in exceptional circumstances as the sentence is also extremely exceptional.