Insanity

• Insanity is the inability to form mens rea, the burden of proof is on the defence
• Insanity was established in M'Naghtens Case in 1843
• There are three elements for insanity to be successful:

  1. Defect of reason
  2. Caused by a disease of the mind
  3. The D does not know the nature and quality of their act, or they did not know what they were doing was legally wrong
• Defect of reason

  • Must be a lack of reasoning, meaning D's powers of reasoning have been impaired - Clarke
• Disease of the mind

  • Must be induced by an internal factor - Kemp
  • Any illness that affects memory, reasoning or understanding caused by an internal source
  • Epilepsy - Sullivan
  • Sleepwalking - Burgess
  • Dissociation - T
  • Diabetes: Hyperglycaemia - Hennessy, Hypoglycaemia is not insanity (Quick)
• D doesn't know

  • The nature and quality of their act - Oye
  • What they were doing was legally wrong - Windle
• A successful defence of insanity can lead to a special verdict of not guilty by reason of insanity
• A successful defence can lead to a range of conclusions up to and including committal to a mental hospital under the Criminal Procedure (Insanity and Unfitness to Plead) Act 1991