Diminished responsibility is a partial defence available only to a charge of murder. Where it succeeds, the defendant is convicted of manslaughter rather than murder, which gives the court discretion over sentence – including a hospital order – in place of the mandatory life sentence.
The test
Section 2 of the Homicide Act 1957, as substituted by section 52 of the Coroners and Justice Act 2009, provides that a person who kills is not guilty of murder if they were suffering from an abnormality of mental functioning which:
- arose from a recognised medical condition;
- substantially impaired their ability to understand the nature of their conduct, to form a rational judgment, or to exercise self-control; and
- provides an explanation for their acts in doing or being a party to the killing – that is, it caused, or was a significant contributory factor in causing, them to carry out that conduct.
The burden of proof lies on the defence, on the balance of probabilities.
“Substantially”
The Supreme Court considered the meaning of “substantially” in R v Golds [2016] UKSC 61. The impairment must be significant and appreciable – more than merely trivial is not enough – and in most cases the jury needs no further direction on the word. Whether the impairment reached that level is for the jury, informed by the psychiatric evidence.
Intoxication
Voluntary acute intoxication is not itself a recognised medical condition and cannot found the defence (R v Dowds [2012] EWCA Crim 281). Alcohol dependence syndrome, by contrast, is a recognised medical condition, and can found the defence. Where a defendant had both an abnormality of mental functioning and was intoxicated, the question is whether the abnormality substantially impaired their abilities and explains the killing, notwithstanding the intoxication (R v Dietschmann [2003] UKHL 10).
How the defence developed
Diminished responsibility began in Scottish law, where a murder charge was reduced because of “weakness of mind” in HM Advocate v Dingwall in 1867. It was introduced into England and Wales by the Homicide Act 1957, when murder still carried the death penalty, as a way of avoiding capital punishment for mentally disordered defendants who did not meet the strict insanity test. The death penalty was abolished in 1965, leaving a mandatory life sentence for murder. The original wording – an “abnormality of mind”, interpreted in R v Byrne [1960] 2 QB 396 – was replaced in 2010 by the current test, which ties the defence to a recognised medical condition and to specific impaired abilities.
What the psychiatric report addresses
A diminished responsibility report takes each element of the statutory test in turn: the diagnosis, and whether it is a recognised medical condition; the nature of the abnormality of mental functioning at the time of the killing; which of the three abilities was impaired, and whether substantially; and whether the abnormality provides an explanation for the defendant’s conduct. It addresses the role of any intoxication, and related issues such as insanity, capacity to form intent and fitness to plead. Where the defence may succeed, it also addresses sentence, including whether a hospital order is appropriate and a bed is available.