Editing M'Naghten rules (section)

===Presumption of sanity and burden of proof===
Sanity is a [[rebuttable presumption]] and the burden of proof is on the party denying it; the standard of proof is on a balance of probabilities, that is to say that mental incapacity is more likely than not. If this burden is successfully discharged, the party relying upon it is entitled to succeed. In Lord Denning's judgement in ''[[Bratty v Attorney-General for Northern Ireland]]'' 1963 AC 386, whenever the defendant makes an issue of his state of mind, the prosecution can adduce evidence of insanity. However, this will normally only arise to negate the defence case when [[automatism (law)|automatism]] or [[diminished responsibility]] is in issue. 

In practical terms, the defence will be more likely to raise the issue of mental incapacity to negate or minimise criminal liability. In ''R v Clarke'' 1972 1 All E R 219 a defendant charged with a [[shoplifting]] claimed she had no ''[[mens rea]]'' because she had absent-mindedly walked out of the shop without paying because she suffered from depression. When the prosecution attempted to adduce evidence that this constituted insanity within the Rules, she changed her plea to guilty, but on appeal the Court ruled that she had been merely denying [[mens rea]] rather than raising a defence under the Rules and her conviction was quashed. The general rule was stated that the Rules apply only to cases in which the defect of reason is substantial.