Diminished responsibility in English law

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For the law in other criminal jurisdictions, see diminished responsibility.

In English law, diminished responsibility operates only as a mitigatory defence to reduce what would otherwise have been murder to manslaughter (termed "voluntary" manslaughter for these purposes). This allows the judge sentencing discretion, e.g. to impose a hospital order under s37 Mental Health Act 1983 to ensure treatment rather than punishment in appropriate cases. Thus, when the actus reus (Latin for "guilty act") of death is accompanied by an objective or constructive version of mens rea, the subjective evidence that the defendant did intend to kill or cause grievous bodily harm because of a mental incapacity will partially excuse his conduct. The burden of proof is on the defendant to the balance of probabilities.

The statutory provision

s2(1) of the Homicide Act 1957 states:

Where a person kills or is party to a killing of another, he shall not be convicted of murder if he was suffering from such abnormality of mind (whether arising from a condition of arrested or retarded development of mind or any inherent causes or induced by disease or injury) as substantially impaired his mental responsibility for his acts and omissions in doing or being a party to the killing.


Abnormality of mind

The defence potentially includes a wide range of mental disorders, provided that the disorder results from :

  • a condition of arrested or retarded development;
  • any inherent causes; or
  • disease or injury.

Thus, the scope is wider than a medical definition of mental illness because the M'Naghten Rules only apply to mental conditions which affect the accused’s cognitive processes to such an extent that the person does not know the nature or quality of his or her act, or does not know that that act was wrong. Whereas diminished responsibility requires a substantial impairment caused by an abnormality of mind which may cover not only abnormalities of perception or cognition, but also an abnormality affecting the ability to exercise will power, and extreme emotional states falling outside the medical definitions of illness and abnormality. Although the effects of voluntarily consuming alcohol or drugs are excluded, it does cover diseases such as delirium tremens caused by long-term alcoholism or drug-taking if the resulting condition causes an impairment of judgment and emotional responses, or the drinking or drug taking becomes involuntary (see R v Tandy (1988) 1 AER 267). In R v Byrne (1960) 2 QB 396 the defendant was a sexual psychopath who strangled a young woman and mutilated her body. Lord Parker CJ defined abnormality of mind as

a state of mind so different from that of ordinary human beings that a reasonable man would term it abnormal. It appears...to be wide enough to cover the mind’s activities in all its aspects, not only the perception of physical acts and matters, and the ability to form a rational judgment as to whether an act is right or wrong, but also the ability to exercise will-power to control physical acts in accordance with that rational judgment.

Whether a defendant is suffering from an "abnormality of mind" is a question for the jury having heard the medical evidence and all the evidence including the defendant's acts or statements. Hence, it has been pleaded with success in cases involving mercy killings, deserted spouses or disappointed lovers who kill while in a state of depression (once referred to as the "Othello syndrome"), reactive depressions, chronic anxiety states, alcoholism, women suffering from "pre-menstrual syndrome", and "battered woman syndrome" so long as the condition is verified as "real" by medical experts.

R v Shickle (2005) EWCA Crim 1881 the defendant stabbed a diabetic several times with syringes full of insulin. The defence denied that excess insulin was the cause of death and adduced evidence that insulin, even in excess, is not a toxic substance which causes death. Further, although Shickle could not remember having injected the deceased, it was possible that she had done so under the impression that he needed insulin and that she had, in her confused state, administered an overdose. Because these explanations were not consistent with a plea of diminished responsibility, the defence was not raised. Two later psychiatric examinations claimed that she suffered from a severe emotionally unstable personality disorder that prevented her from admitting the facts necessary to substantiate diminished responsibility. Reviewing the authorities on whether to accept fresh evidence to support a plea that was not advanced at the trial, the Court of Appeal noted that in R v Ahluwalia (1993) 96 Cr. App. R .133 Lord Taylor observed that:

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.

The effect of the abnormality

The abnormality of mind must substantially impair, but need not totally impair, the defendant's mental responsibility. As in Byrne, the defendant may understand the nature and quality of what he is doing, and/or know that it is wrong, and may have some degree of control over himself. In R v Egan (1992) 4 AER 470, it was held that "substantial" impairment was the kind of word that could be interpreted in a broad common sense way. Hence, it meant that there was:

...more than some trivial degree of impairment which does not make any appreciable difference to a person's ability to control himself, but it means less than total impairment.

The relationship to drunkenness and drug taking

Drunkenness cannot be a defence to manslaughter or any other crime of basic intent, and the fact that a defendant might have been drunk at the time of committing a murder is also irrelevant to support a plea of diminished responsibility because it is an "external" not an "inherent cause" within s2. In R v Gittens (1984) QB 698 a defendant who suffered from depression killed his wife and stepdaughter after drinking and taking drugs for medication. The direction to a jury facing both diminished responsibility and drunkenness should be:

  • Would the defendant have killed as he did if he had not been drunk?

and if the answer to that is yes,

  • Was he suffering from diminished responsibility when he did so?

The more chronic forms of alcoholism and the long-term use of heroine and cocaine (see R v Sanderson (1994) 98 Cr. App. R. 325) can become a relevant factor where a craving for drink or drugs causes an abnormality of mind. This must be distinguished from the situation in which the abnormality of mind causes a craving for drink or drugs . R v Tandy (1989) 1 AER 267 held that where a defendant could show that she was suffering from an abnormality of the mind, that it was induced by disease (namely alcoholism), and that it substantially impaired her responsibility for her actions, then the defence of diminished responsibility would be made out. In the actual case, the craving for alcohol did not render the use of alcohol involuntary. The defendant was in control when she began drinking, and the state of mind in which she killed her daughter was merely induced by the alcohol. In R v Dietschmann (2003) UKHL 10, the House of Lords held that where a defendant suffers from an abnormality of mind within s2(1) also consumes alcohol before the killing, the jury should find him or her guilty of manslaughter if they are satisfied that, notwithstanding the alcohol consumed and its effect, the abnormality of mind substantially impaired the mental responsibility for the fatal acts. The sub-section does not require the abnormality of mind to be the sole cause of the defendant’s acts; even if the defendant would not have killed if he had not consumed alcohol, the causative effect of the alcohol does not prevent an abnormality of mind suffered by the defendant from substantially impairing his mental responsibility for the fatal acts.


  • Boland, F. (1995). "Diminished Responsibility as a Defence in Irish Law". 5 Irish Criminal Law Journal 193.
  • Boland, F. (1996). "Diminished Responsibility as a Defence in Irish Law: Past English Mistakes and Future Irish Directions". 6 Irish Criminal Law Journal 19.
  • Butler Committee (1975) The Butler Committee on Mentally Abnormal Offenders (London: HMSO) Cmnd 6244.
  • Dell, S. (1982). "Diminished Responsibility Reconsidered". Criminal Law Review 809.
  • Griew, E. (1986). "Reducing Murder to Manslaughter: Whose Job? 12 Journal of Medical Ethics 18.
  • Griew, E (1988). "The Future of Diminished Responsibility". Criminal Law Review 75.