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. That matters enormously: murder carries a mandatory life sentence, while for manslaughter the court has full discretion over sentence, including a hospital order.
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 do one or more of three things – to understand the nature of their conduct, to form a rational judgment, or to exercise self-control; and
- provides an explanation for their acts and omissions in doing or being a party to the killing.
An abnormality provides an explanation if it causes, or is a significant contributory factor in causing, the defendant to carry out that conduct. The burden of proof lies on the defence, on the balance of probabilities.
The elements in turn
Abnormality of mental functioning
The focus is on how the defendant’s mind was actually working at the time, not simply on their diagnosis. The psychiatric evidence must describe that functioning and link it to the killing.
A recognised medical condition
This ties the defence to accepted diagnoses, usually those in the international classifications such as ICD and DSM. Psychotic illnesses, mood disorders, personality disorders, autism, intellectual disability, brain injury and alcohol dependence syndrome can all qualify. Appearing in a classification is not always enough, however: voluntary acute intoxication is not a recognised medical condition for this purpose, even though classifications describe it (R v Dowds [2012] EWCA Crim 281).
Substantial impairment
The Supreme Court considered “substantially” in R v Golds [2016] UKSC 61. The impairment must be important or weighty – an impairment that is merely more than 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.
Which abilities
The three abilities are alternatives: it is enough that one was substantially impaired. In practice, psychotic illness most often bears on understanding and rational judgment; mood and personality disorders, intellectual disability and brain injury more often on rational judgment and self-control. The report should say which ability was impaired, how, and why.
An explanation for the killing
The abnormality need not be the only cause of the defendant’s conduct, but it must be a significant contributory factor. A defendant with a recognised condition who killed for reasons unconnected with it cannot rely on the defence.
Intoxication and dependence
Intoxication is the commonest complication. Three principles apply:
- Voluntary acute intoxication is not itself a recognised medical condition and cannot found the defence (Dowds).
- Alcohol dependence syndrome is a recognised medical condition, and can found the defence where the other elements are met.
- Where a defendant had an abnormality of mental functioning and was also intoxicated, the question is whether the abnormality substantially impaired their abilities and explains the killing, notwithstanding the intoxication (R v Dietschmann [2003] UKHL 10). The jury must set the effect of the intoxication aside.
Separating the effects of illness, dependence and acute intoxication at the time of a killing is among the most difficult tasks in forensic psychiatry, and the report should be explicit about how it has done so.
Sentence after a manslaughter verdict
Following a conviction for manslaughter by reason of diminished responsibility, sentence is governed by the Sentencing Council’s guideline for that offence, which places weight on the defendant’s level of retained responsibility. Where the defendant has a mental disorder requiring treatment, the court will consider a hospital order under section 37 of the Mental Health Act 1983, with or without a restriction order under section 41; a hospital and limitation direction (“hybrid order”) under section 45A; or imprisonment. The Court of Appeal gave guidance on choosing between these in R v Vowles [2015] EWCA Crim 45. The psychiatric evidence on treatment, risk and the availability of a bed is often decisive.
Diminished responsibility and loss of control
Loss of control, under sections 54 to 56 of the Coroners and Justice Act 2009, is the other partial defence to murder. It turns on a loss of self-control with a qualifying trigger, judged against a person of the defendant’s sex and age with a normal degree of tolerance and self-restraint. Psychiatric evidence plays a much more limited part, but both defences are often run together, and the report may need to address the relationship between them.
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 test for insanity. The death penalty for murder was abolished in 1965, leaving the mandatory life sentence. The original wording – an “abnormality of mind”, interpreted broadly 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 intoxication and dependence explicitly, considers related issues such as insanity, intent, loss of control and fitness to plead, and – where the defence may succeed – addresses sentence, including whether a hospital or hybrid order is appropriate and a bed is available.