⇒ It is crucial to distinguish between two different claims in relation to insanity:

1. A claim that a defendant was insane at the time he or she committed the offence.
2. A claim that the defendant was insane at the time of the trial and so unable effectively to defend him or herself.

⇒ The issue of the defendant's insanity at the time of the crime can be raised in three ways:

1. The defendant straightforwardly claims he or she was insane at the time of the offence.
2. The defendant raises a defence of no mens rea or automatism, but the judge decides that the evidence discloses a defence of insanity. The judge may then instruct the jury to consider the issue of insanity.
3. If the defendant raises a plea of diminished responsibility then the prosecution is entitled to rebut the defence by producing evidence of insanity.

⇒ A defendant who wishes to plead that he or she was insane at the time of the offence must demonstrate that he or she was suffering from a defect of reasoning caused by a disease of the mond which meant that either:

1. he or she did not know the nature or quality of his or her actions; or
2. he or she did not know that what he or she was doing was wrong.

⇒ See the case of R v Sullivan [1984].

⇒ The phrase 'disease of the mind' is to be given its normal meaning: it is not a medical term.

⇒ This means that diabetes, for example, can amount to a disease of the mind if it produces a malfunctioning of the brain.

⇒ Lord Denning in R v Bratty [1963] suggested that a disease of the mind was a mental disorder which manifested itself in violence and was prone to reoccur. However, these dicta have since been rejected and it is clear that a 'disease of the mind' need not be prone to recur nor manifest itself in violence.

⇒ It must be shown that the disease of the mind gave rise to a defect of reason: the defendant's power of reasoning must be impaired.

⇒ Not knowing the nature and quality of the act would be so in the following situations:

1. The defendant had no awareness of what was happpening e.g. having a seizure
2. The defendant was aware what he or she was doing, but was deluded as to the material circumstances of his or her actions, rendering the act fundamentally different.
3. A person who was unaware of the consequences of his or her act, for example he or she was unaware that his or her act would kill the victim.

⇒ Not knowing the act is wrong means that the defendant did not know his acts were illegal (R v Windle [1952]).

⇒ In DPP v Harper [1998] it was held that insanity was not a defence to a strict liability offence.

⇒ However, most commentators take the view that the decision is wrong.

⇒ In summary the defendant's mental capacity must be sufficient for him or her to be able to conduct his or her defence adequately.

⇒ In R v Moyles [2009] it was explained that this meant a defendant could have the capacity to stand trial, even if his or her mental condition meant that he or she thought there were 'evil influences' at work in the trial.

⇒ In R v Podola [1960] a controverisal decision was reached: the defendant who suffered a condition which makes him forget event was held to be fit to plead in court.