Diminished responsibility in English law


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

In English law, diminished responsibility is one of the partial defences that reduce the offence from murder to manslaughter if successful (termed "voluntary" manslaughter for these purposes). This allows the judge sentencing discretion, e.g. to impose a hospital order under section 37 of the 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 (Latin for "guilty mind"), 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 M'Naghten Rules lack a volitional limb of "irresistible impulse"; diminished responsibility is the volitional mental condition defence in English criminal law.

The statutory provision
Section 2(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.

The defence has recently been amended by s. 52 of the Coroners and Justice Act 2009.

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, 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 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: and if the answer to that is yes, The more chronic forms of alcoholism and the long-term use of heroin and cocaine (see R v Sanderson ) 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 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, 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. Dietschmann was later applied by the Court of Appeal in R v Hendy.
 * Would the defendant have killed as he did if he had not been drunk?
 * Was he suffering from diminished responsibility when he did so?