Consideration of the meaning of “substantially impaired” in diminished responsibility cases.
The appellant was convicted of murder. The primary issue at his trial had been whether he satisfied the test under s.2(1)(b) of the Homicide Act 1957, as amended by the Coroners and Justice Act 2009, for the partial defence of diminished responsibility.
The trial judge had provided the jury with a written summary of the elements of diminished responsibility, but refused to define "substantially" in the phrase "substantially impaired", unless the jury requested assistance, which they did not.
Upon appeal  EWCA Crim 748, it was originally submitted that (1) the trial judge had been wrong not to direct the jury on the meaning of "substantially impaired" and (2) the jury might, in the absence of a direction, have applied a more stringent test than it ought to have done. It was submitted on behalf of the appellant that so long as the impairment was more than merely trivial, the test of "substantially impaired" was met.
The Court of Appeal had dismissed the appeal on the basis that (1) the judge was not required to give further definition and (2) if he had done so the appropriate formulation would have been that it was not enough that there was some impairment; the jury must ask if it was substantial.
The appellant appealed to the Supreme Court (the Court).
The Court unanimously dismissed the appeal.
A thorough review of the authorities was conducted and particular attention was paid to the case of R v Lloyd  1 QB 175. The Court concluded that in the context of diminished responsibility, "substantially" has always been held to mean "important or weighty".
In response to the grounds argued in the Court of Appeal, the Court held as follows:
1) The judge need not direct the jury beyond the terms of the statute and should not define the meaning of "substantially". The jury should understand that word as an ordinary English word, it is a matter for them to decide if the impairment can properly be described as substantial.
2) If the jury have been introduced to the question of whether any impairment beyond merely trivial will suffice, or if the concept of a spectrum has been employed, the judge should explain that whilst the impairment must be more than merely trivial before it need be considered, it is not the law that any impairment beyond the trivial will suffice.
Finally, the Court held that the appellant's case did not rest upon the meaning of "substantially". Instead, the real question on the evidence adduced at trial should have been whether, on the balance of probabilities, the appellant had been suffering an impairment at all and the trial judge had correctly left this issue to the jury. The appeal was dismissed.
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