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Criminal | Defences

Insanity: Criteria

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[Flash Card 1 of 2]

  • D must prove / on balance of probabilities / insane at time of offence / available all offences which require mens rea
  • if successfully argued /special verdict / not guilty by reason of insanity / judge make order (Criminal Procedure (Insanity and Unfitness to Plead) Act 1991)
  • M'Naghten rules / require three elements / defect of reason / as result of disease of the mind / causes D not to know nature & quality of his act or it was wrong

Defect of Reason:

  • D's reasoning impaired, / inability to use powers of reasoning / not merely failure to do so
  • temporary confusion or absent mindedness / not defect of reason (Clarke)

Disease of the Mind:

  • legal term / not medical / law concerned whether D can be held liable / not medical condition
  • disease of mind must physical / not brought on by external factors / eg drugs
  • no express definition / case law developed meaning
  • may be sufficient / temporary insanity (Kemp) / reoccurring violent tendencies (Bratty) / sleep disorders (Burgess)
  • source of the disease / irrelevant (Sullivan)
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[Flash Card 2 of 2]

Defendant's Knowledge:

  • D's disease of mind / must cause D not to know / nature and quality of his act / or his act was wrong

Nature and quality:

  • refers to physical character of the act / prove D did not know what he was doing / or appreciate consequences / or circumstances in which acting
  • if D can prove did not know nature and quality / D lacks sufficient mens rea


  • D may know nature and quality / but not realise it is wrong / so have the necessary mens rea / but because of insanity not realise wrong / can use insanity defence
  • if D knew unlawful to kill defence unavailable (Codere) / wrong means contrary to the law (Windle) /difference between legally & morally wrong not recognised
  • in Johnson / CoA noted Australian decision / found D could be acquitted even if knew act legally wrong / but believed morally right / CoA highlighted: .. difficulties and internal inconsistencies which can arise from the application of the M'Naghten rules if the decision in Windle is correct... / but bound to follow Windle
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