The Court of Appeal held that because the evidence showed that for periods of the journey D was in some control, D had been driving without due care and attention, and was not an automaton.

That was an internal cause (the diabetes itself) and not an external cause (the insulin). The correct defence was insanity.

Although the Court of Appeal had allowed D’s appeal because of the apparent absence of moral fault, the House of Lords held where the prosecution proved that the mens rea was present when the actus reus occurred, the defence of involuntary intoxication could not be open to D.

If D is charged with a specific intent crime and did not form mens rea, he is not guilty of that crime (but liability may be reduced). Voluntary intoxication is not a defence to basic crimes (+ the Richardson and Irwin ‘gloss’; if D would have formed the mens rea when sober).

The House of Lords stated: ‘the jury should be directed that every man is presumed to be sane … until the contrary be proved to their satisfaction, and that to establish a defence on the ground of insanity it must be clearly proved that at the time of committing the act the party accused was labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing, or, if he did know it, that he did not know that he was doing what was wrong.’

The House of Lords held that a defendant cannot be convicted of rape if he believed, albeit mistakenly, that the woman consented, even though he had no reasonable grounds for that belief (the reasonableness or otherwise of the alleged belief was important evidence as to whether or not it was truly held).

The Court of Appeal held that ‘disease of the mind’ within the meaning of the M’Naghten Rules was a malfunctioning of the mind caused by disease. It did not include the application to the body of some external factor, such as insulin.

The House of Lords accepted that it was regrettable that the label of insanity had to be applied to a case of epilepsy, but D had an internal disorder which impaired D’s mental faculties of reason, memory, and understanding.