M’Naghten Rules – defence of insanity
August 1, 2022
1. The Court of Appeal has recently considered the defence of insanity and has revisited the rules established in Daniel M’Naghten’s case (1843) C & F 200. The House of Lords, in a procedure available to them as a legislative body at that time, were asked questions about the approach of the criminal courts when a defendant did an act that amounted to a crime but was insane at the time. A defendant is presumed by law to be sane and accountable for his actions unless the contrary is proved. It is for a defendant to establish the defence of insanity on a balance of probabilities and the inaptly named Trial of Lunatics Act 1883 provides for the special verdict of not guilty by reason of insanity.
2. The principles, in summary form, are as follows;
i. Every man is presumed to be sane unless the contrary is proved
ii. To establish the defence of insanity it must be proved that at the time of committing the act the defendant was labouring under a defect of reason from a 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 what he was doing was wrong.
iii. Every man is presumed to know the law of the land.
iv. A suitably qualified expert is entitled to give his opinion.
3. The Court of Appeal considered these rules in Keal  EWCA Crim 341 where the appellant was convicted of the attempted murder of his grandmother, father and mother. He had a long history of mental health problems and in the weeks leading up to the attacks had exhibited extremely bizarre behaviour. The day before the attacks he attempted suicide and was taken to hospital. The evidence in the case set out that during the attack on his mother the defendant said ‘I’m sorry this is not me it’s the devil’. When trying to kill his father he said ‘I’m sorry I don’t want to I’m sorry I’m sorry dad.’ After the attacks he was found by the police on a lane dressed only in his underpants
4. The defence pleaded that the appellant was insane at the time of the acts and was operating under multiple delusions including a belief that he was possessed by the devil. He didn’t give evidence at his trial because he was too unwell but the jury heard from 4 psychiatrists, two for each side. The issue the jury had to decide, and the area of disagreement between the psychiatrists, focused on the extent the appellant’s disordered mental state impaired his ability to know that what he was doing was wrong.
5. The trial Judge directed the jury that ‘For the defence to be made out in this case the defence must satisfy you that it was more likely than not at the time of the assaults on his parents and grandmother, Jonathan Keal did not know that what he was doing was wrong, in the sense that it was against the law. That means that you are concerned with what was or was not in Jonathan Keal’s mind at the time. In the route to verdict document the first question was “Is it more likely than not that the defendant did not know that his actions on the night of the 26-27th September 2018 were against the law? If the answer was ‘yes’ then the defendant would be not guilty by reason of insanity. He was found guilty on all 3 counts.
6. The Court of Appeal endorsed the trial Judge’s approach. They held at paragraph 41 that in order to establish the defence of insanity on the ground of not knowing that the act was wrong the defendant must establish both that (i) he did not know the act was unlawful (ie contrary to law) and (ii) that he did not know that his act was morally wrong (also expressed as wrong by the standards of ‘ordinary’ people). Thus the court held that wrong means both against the law and wrong by the standards of ordinary reasonable people.
7. There is a body of opinion that the defence as currently framed is out of line with modern psychiatric thinking. The Court of Appeal referred to the Law Commission’s discussion paper ‘Criminal Liability: Insanity and Automatism (2013)’. In that paper the Commission proposed a wholly new defence whereby someone would be able to plead that they were not criminally responsible by reason of a qualifying medical condition. However, the Court (at paragraph 51) was clear that reform of this area was an issue for Parliament. Thus, we are still no closer to legislation that may clarify a difficult area of law that is often difficult to disentangle, lacks coherence and reflects opinions from 179 years ago.