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Voluntary Manslaughter - Diminished Responsibility
Diminished responsibility is one of three special defences which exist solely for the offence of murder. It is contained in the Homicide Act 1957 as modified by the Coroners and Justice Act 2009. Where the defence of diminished responsibility is successfully pleaded, it has the effect of reducing a murder conviction to manslaughter. The three special defences of diminished responsibility, loss of control and suicide pact differ from general defences in that they do not apply to all crimes and also the effect is to reduce criminal liability rather than to absolve the defendant from liability completely.
Diminished responsibility is set out in s.2 of the Homicide Act 1957 as amended by s.52 of the Coroners and Justice Act 2009. To rely on the defence, the defendant must be able to demonstrate the following: 
  1. An abnormality of mental functioning caused by a recognised medical condition.
  1. Which provides an explanation for the defendant’s acts or omissions in being party to the killing.
  1. Which substantially impaired his/her mental ability to either:

a)      Understand the nature of their conduct or

b)      Form a rational judgment or

c)      Exercise self–control

1. Abnormality of the mental functioning caused by a recognised mental condition.
Prior to the Coroners and Justice Act 2009, the Homicide Act 1957 referred to abnormality of the mind. The change of wording in this respect was simply to clarify the law and is not expected to make any changes to the applicability of the defence. Thus the case law under the Homicide Act, is still helpful in determining what may count as an abnormality of the mental functioning. The question of whether the defendant is suffering from an abnormality of the mental functioning is for the jury to decide after hearing medical evidence. The jury are not bound to follow medical opinion it is ultimately their decision as to whether the defence should succeed. A notorious example of the jury ignoring medical opinion was present in the trial of Peter Sutcliffe (the Yorkshire ripper) where the medical opinion was unanimous that the defendant was a paranoid schizophrenic, yet the jury refused to allow him the defence.  Abnormality of the mental functioning is assessed by reference to what a reasonable man would regard as abnormal. It has a wide meaning and encompasses the inability to exercise will power and control.
R v Byrne (1960) 2 Q.B. 396     Case summary
Some examples of what has been held to constitute an abnormality of the mind include:
  • Jealousy (R v Miller 1972,even unfounded jealousy R v Vinagre 1979)
  • Battered woman syndrome (R v Hobson 1997, R v Ahluwalia 1993)
  • Pre-menstrual tension (R v Smith 1982, R v Reynolds 1988)
  • Epilepsy (R v Campbell 1997)
  • Chronic depression (R v Seers, R v Gittens 1984)
In each case the defendant must demonstrate that the characteristic was excessive when compared to that experienced by a reasonable person.
2. The abnormality must provide an explanation for D’s act or omission in being party to the killing.

This is an issue of causation - S. 1B Homicide Act 1957 states that an abnormality of the mental functioning provides an explanation for D's Conduct if it causes or is a significant contributory factor in causing D to carry out that conduct. This follows from the old law under S.2 Homicide Act 1957 which required the abnormality to be caused by an arrested or retarded development of the mind or any inherent causes or induced by disease or injury. This was interpreted by the courts as meaning that the abnormality must be caused by an inside source and that outside factors causing the abnormality such as alcohol or drugs could not be taken into account unless the abnormality was as a result of the disease of alcoholism or drug addiction or long term damage caused by the intake of such intoxicants: 

R v Tandy [1989] 1 WLR 350   Case summary
R v Wood [2009] 1 WLR 496   Case summary
R v Stewart [2009] 1 WLR 2507 Case summary
The same approach is applied where the defendant is intoxicated by prescription drugs:
R v O'Connell 1997 Crim LR 683
Where there exists an abnormality of the mind in addition to intoxicants, the legal position was stated in R v Gittens and affirmed in R v Dietschmann:
R v Gittens (1984) 79 Cr App R 272    Case summary
 R v Dietschmann [2003] 1 AC 1209  Case summary  

Acute voluntary intoxication (binge drinking) alone is not capable of founding the defence of voluntary intoxication:

R v Dowds [2012] EWCA Crim 281   Case summary

3.Which substantially impaired his/her mental ability

The defendant must show that the abnormality of the mind must have substantially impaired his mental ability to either:

  • Understand the nature of their conduct or
  • Form a rational judgment or
  • To exercise self –control
This is a question for the jury to decide after hearing medical evidence. It is not necessary to show a complete loss of control, however, any evidence of planning on the part of the defendant may be used to show the defendant’s mental ability was not impaired.
R v Campbell [1997] 1 Cr App R 199    Case summary 
Raising diminished responsibility on appeal
If the defendant did not raise the defence of diminished responsibility at trial, the appeal courts are reluctant to admit fresh evidence relating to diminished responsibility:
R v Andrews [2003] EWCA Crim 2750         Case summary

In the case of R v Ahluwalia [1993] 96 Cr App. R. 133   Case summary Lord Taylor CJ stated:

    "Ordinarily, of course, any available defences should be advanced at trial. Accordingly, if medical evidence is available to support a plea of diminished responsibility, it should be adduced at the trial. It cannot be too strongly emphasised that this court would require much persuasion to allow such a defence to be raised for the first time here if the option had been exercised at the trial not to pursue it. Otherwise, as must be clear, defendants might be encouraged to run one defence at trial in the belief that if it fails, this court would allow a different defence to be raised and give the defendant, in effect, two opportunities to run different defences. Nothing could be further from the truth. Likewise, if there is no evidence to support diminished responsibility at the time of the trial, this court would view any wholly retrospective medical evidence obtained long after the trial with considerable scepticism.
In deciding whether to admit fresh evidence the court must have regard to S. 23 of the Criminal Appeal 1968 which provides:
"(1) For purposes of this Part of this Act the Court of Appeal may, if they think it necessary or expedient in the interests of justice --
(c) receive any evidence which was not adduced in the proceedings from which the appeal lies.
(2) The Court of Appeal shall, in considering whether to receive any evidence, have regard in particular to --
(a) whether the evidence appears to the Court to be capable of belief;
(b) whether it appears to the Court that the evidence may afford any ground for allowing the appeal;
(c) whether the evidence would have been admissible in the proceedings from which the appeal lies on an issue which is the subject of the appeal; and
(d) whether there is a reasonable explanation for the failure to adduce the evidence in those proceedings."
The court is particularly reluctant to allow fresh evidence if the decision not to raise the defence of diminished responsibility was made for tactical reasons as oppose to reasons relating to the capacity to instruct the defence:
R v Erskine [2009] EWCA Crim 1425    Case summary
R v Neaven [2006] EWCA Crim 955    Case summary
R v Diamond [2008] EWCA Crim 923 Case summary 
R v Hendy [2006] EWCA Crim 819            Case summary
R v Martin [2002] 2 WLR 1         Case summary
The courts are more willing to admit fresh evidence relating to diminished responsibility where there have been advances in medical opinion since the time of trial:
R v Ahluwalia [1993] 96 Cr App. R. 133   Case summary 
R v Hobson [1997] EWCA Crim 1317        Case summary
R v Campbell [1997] 1 Cr App R 199    Case summary  
Further reading:

Law Commission Report - Partial defences to murder 2004