• To establish a defense of not guilty by reason of insanity under the M’Naghten rules, the accused must show that they were deprived of the power of reasoning due to a disease of the mind.

Facts of the Case

  • The accused (C) was on trial for shoplifting.
  • C admitted to taking the goods but claimed it was due to suffering from diabetes, which caused absentmindedness and depression.
  • The judge ruled that a defense of insanity was raised, but C pleaded guilty to avoid being labeled insane.

Issues in R v Clarke 1972 1 ALL ER 219

  • Could absentmindedness be considered a defense for theft?
  • Could the conviction be quashed due to C pleading guilty based on the judge’s ruling?

Decision of the Court (Court of Appeal)

  • The appeal was allowed, and the conviction was quashed.


  • The defense of absentmindedness amounted to a defense of not guilty by reason of insanity within the M’Naghten rules.
  • On appeal, it was determined that there was no sufficient defect of reason as C still retained her ordinary powers of reason.

Quote from one of the judges: “It is not sufficient for the defence that the prisoner was not thinking as clearly or reasonably as a reasonable person would think. There must be a defect of reason, total deprivation of the powers of reason” – Lord Justice Lawton.