By Paul Harvey
Scotland: Appeal Court, High Court of Justiciary
Diminished responsibility — test for diminished responsibility when accused has both a mental disorder and has taken alcohol/drugs
Balance of probabilities — whether it was an error to direct the jury in percentage terms.
Nicholas Rogers v Her Majesty’s Advocate
 HCJAC 27
NR was convicted of murder by stabbing. He suffered from Emotionally Unstable Personality Disorder/Borderline Personality Disorder but had also been drinking and had taken drugs at the time of the offence. The issue at trial was whether the defence of diminished responsibility was made out.
The trial judge directed the jury that, in considering that issue, they had to consider whether the appellant’s personality disorder or the alcohol//drugs was the substantial cause of his actions. He further directed the jury that the test of whether diminished responsibility had been established was on the balance of probabilities. Having said that this was something that was more probable than not, he added that, “put it into percentage terms, something is more likely than not if it’s 51% playing 49%”.
NR appealed on the ground that these were material misdirections. For the first, the accused did not have to show that the mental disorder was the substantial cause of his actions, only that it remained a substantial cause. For the second, as Toulson LJ (as he then was) explained in Milton Keynes Borough Council v Nulty  1 WLR 1183 at para , it was wrong and “pseudo-mathematical” to seek to define balance of probabilities in percentage terms, and judges should not attempt to elaborate on the clear and ordinary meaning of “more probable than not”.
The Court dismissed the appeal on the facts but found:
- The judge erred in his direction on diminished responsibility. It should not have been a question of the two possible causes (mental disorder or alcohol/drugs) being alternatives. The trial judge’s use of “the” rather than “a” when referring to substantial cause created the error. All that the jury had to be told in relation to the possible combination of causes was that they could find diminished responsibility if they were satisfied on the balance of probabilities that, despite the drink, the accused’s mental abnormality substantially impaired his ability to determine or control his conduct (Lord Hutton’s model direction in R v Dietschmann  1 AC 1209). The proper approach was to discount the effect of the drink and drugs, both on their own or by reason of their combination with the appellant’s underlying mental disorder. The question in practical terms was: if the appellant had not ingested the alcohol/drugs which he did, would he have acted as he did and delivered the fatal blow as a consequence of his mental abnormality?
- It could be dangerous to attempt to reduce the exercise of determining whether something is more likely than not to have happened to one of combined arithmetical possibilities. Nevertheless, using it in this case would not have led the jury to misunderstand the meaning of probabilities. It was not a substantially erroneous description.
- This is a Scottish case, but since the law of England and Wales on diminished responsibility originated in, and borrowed heavily from, Scots law (see R v Golds  UKSC 61), this case may be of broader significance to the development of diminished responsibility in England and Wales. The Appeal Court’s judgment clarifies that juries need only be directed that they can find the defence of diminished responsibility established if they are satisfied that, despite the drink, the accused’s mental abnormality substantially impaired his ability to determine or control his conduct. This should be a straightforward direction to give and, to that extent, provides welcome clarification. But it may prove difficult for juries to apply in cases where, as here, a psychiatrist giving expert evidence finds it difficult after the event to separate a psychiatric cause for someone’s actions from other possible causes, and thus decline to speculate on what would have happened had the person not taken drink/drugs.
- The second ground of appeal is perhaps an indication that, beyond saying that balance of probabilities means more likely than not, any further attempt to define it is highly undesirable and that any attempt to introduce mathematical terminology will risk the kind of criticisms the late Lord Toulson set out a length in Milton Keynes Borough Council v Nulty.
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