Chapter 14 Key facts checklists

In this chapter we examine age, insanity, automatism, intoxication, and mistake.
If under the age of ten, D is deemed incapable of criminal liability.
Insanity is where D proves he or she had a disease of mind which caused a defect of reason
so that D did not know the nature and quality of his or her act or that it was wrong. If the disease of mind was due solely to an external cause, the defence is non-insane automatism rather than insanity.
Non-insane automatism is an assertion by D that the prosecution cannot prove the actusreus of the offence because D was not in control of his or her muscular movements. D has to raise evidence of this and the prosecution has to disprove it.
Intoxication is never a defence in itself. However involuntary intoxication can be relied upon as evidence that D lacked the mens rea needed for the particular crime. In such a case, D will be acquitted because they lacked the mens rea, not because of intoxication.
Voluntary intoxication can also be relied upon as evidence of a lack of mens rea, but only in offences of specific intent (where intention is the mens rea). It cannot be used as evidence in cases of basic intent (where recklessness is the mens rea). Indeed, in cases of basic intent a voluntarily intoxicated defendant will be deemed reckless on the basis they would have foreseen the result had they been sober.
Mistake is a defence in cases where the mistake prevents D forming mens rea.
As you can see from this list, most defences are actually negative assertions, which means that D is alleging the prosecution cannot prove a definitional element of the offence (actus reus or mens rea).
The burden of disproof in relation to the defences usually lies on the prosecution.