A2 Law - Defences (Insanity and Consent) Evaluation

Evaluation of the general defences: consent and insanity. 

  • Created by: Sarah
  • Created on: 22-01-12 15:51


  • The Law Commission issued a Consultation Paper in 2008: 'Unfitness to Plead and Insanity Defence'. This outlines issues with the defence of insanity, including its antiquity, the definition of 'disease of the mind', and the overlap with the defence of automatism. 

The next cards look more specifically at the problems with the defence of insanity. 

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  • The defence of insanity is found in the M'Naghten rules. These were devised by judges in 1843 when psychiatric illness was barely understood. Today an insanity plea must still satisfy those legal rules, despite massive developments in psychiatric understanding. 
  • In 1953, based on medical opinion, the Royal Commission on Capital Punishment described the M'Naghten rules as 'obsolete and misleading'. They also said that the 'disease of the mind' element is outdated and inaccurate.   
  • The legal definition is also changing constantly through case law developments. Although this allows for the M'Naghten rules to be overlooked in certain situations where the rules would be inappropriate to apply, it does create inconsistencies and confusion within the law. For example, Lord Denning stated that the mental disorder must be 'prone to recur', yet in Burgess, Lord Lane stated that it need not be 'prone to recur'. 
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  • The law has also been criticised as too wide, as it includes illnesses such as epilepsy (Sullivan), sleep-walking (Burgess), and diabetes (Hennessy). 
  • Yet, it has also been criticised as too narrow. This is because it can exclude those who are clinically but not legally insane. The 'defect of reason' test excludes those who know what they are doing but are unable to control themselves (Byrne). 
  • Another huge problem with the definition is that is has become entirely legal and not medical. A psychiatrist would argue that a person may understand their actions yet still be mentally ill. However, legally, a person would still be accountable if they understood their actions. 
  • Another issue is that physical conditions (e.g. arteriosclerosis in Kemp) can constitute insanity, however mental conditions (e.g. irresistible impulses in Byrne) may not. Denying mental but permitting physical conditions is absurd. 
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  • Another problem is that there can often be conflicting psychiatric expert opinions. As a result, medically unqualified jurors will have to decide whether someone is legally insane or not when choosing between these opinions. 
  • Detaining defendants who are epileptics, diabetics or sleepwalkers could be in breach of the ECHR Article 5 (the right to liberty). In Winterwerp v Netherlands, the ECHR ruled that whether someone is of unsound mind is a matter of objective medical expertise. The M'Naghten rules conflicts this ruling, as in England, insanity is based on the legal definition. 
  • Approximately a third of all prisoners are believed to suffer from some form of medical disorder, but for those prisoners, the insanity verdict was not available. The law in this respect is applied unfairly. 
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  • The law on insanity also overlaps with automatism. This has serious consequences as those using the defence of automatism are entitled to a complete acquittal. Whereas those found not guilty by reason of insanity will be imposed with an order. The seriousness of the consequences can be illustrated by the condition, diabetes, which can sometimes lead to the defence of insanity, if it is caused by an internal factor (Hennessy), or automatism, if the offence is caused by an external factor (Quick). 
  • Lastly, the word 'insanity' itself carries a social stigma. Psychologically speaking, we do not often refer to patients as insane any more.
  • One development of the defence of insanity, which can now be seen as an advantage, is that those found not guilty by reason of insanity can be given either a hospital order, treatment order or absolute discharge. This is better than the old rule, whereby a defendant who successfully pleaded insanity would be detained indefinitely. This means that defendants like Quick could receive treatment or an absolute discharge, as people with diabetes generally pose no threat to society. To detain them indefinitely would be unfair. 
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Insanity - Reforms

  • In 1953, the Royal Commission on Capital Punishment suggested that the M'Naghten rules should be extended so a defendant should be considered insane if he 'was incapable of preventing himself' from committing the offence. This means that those suffering from 'irresistible impulses' would fall within the definition. Instead the government introduced the defence of diminished responsibility. Byrne illustrates the success of this defence as, although the D knew what he was doing was wrong, but he was compelled by irresistible impulses. He would not be able to rely on insanity as he knew what he was doing, but was able to reply on diminished responsibility to reduce his sentence to one of voluntary manslaughter. 
  • This new defence also allows for people to branch away from the social stigma that the word 'insanity' carries, as well as allowing them to not be hospitalised, but imprisoned instead - some people would see this as a better option. 
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Insanity - Reforms

  • In 1975, the Butler Committee suggested that the verdict of not guilty by reason of insanity should be replaced by a verdict of not guilty on evidence of mental disorder. This solves the issue of the social stigma surrounding the word 'insanity'. They also propose that someone who knows what they were doing, but could not prevent themselves due to mental disorder, would be allowed to use the defence. 
  • In 1989, the Law Commission's Draft Criminal Code proposed that a defendant should be 'not guilty on evidence of severe mental disorder or severe mental handicap'. 

None of these proposals have been made law yet. 

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  • It is hard to reconcile the decisions made by the courts in consent cases. For example, in Brown the HOL held that consent could not be a defence to sado-masochistic activities between consenting adult homosexuals causing s.47 and s.20 injuries, unless it was a recognised exception. Yet in Wilson, consent was a defence when a husband branded his initials into his wife's buttocks. Medical assistance was needed in Wilson, but not in Brown, yet consent was not allowed in Brown, but it was in Wilson.
  • Was this because they were homosexuals? Are the law lords imposing their own moral views on the law? 
  • In Emmett, it was held that consent cannot be a defence if the harm caused was more than 'transient or trivial', yet in Wilson, where medical attention was needed, consent was allowed. 
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  • Courts will accept consent as a defence to horseplay. Although this is an advantage, as the courts have recognised that mainly boys often engage in rough and undisciplined horseplay, the courts have allowed some extreme cases, where serious injury has been caused, such as the 35% burns caused to the victim in Aitken. Courts have even accepted cases where the victim did not consent, such as in Jones. 
  • A person cannot consent to their own death (Pretty). 
  • However, in the case of a mercy killing, it is unlikely that someone will receive a 'whole life' tariff. They can often use the defence of diminished responsibility. 
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BeckyLou X


Very useful to use as additional notes! :) 

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