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Manslaughter by Reason of Diminished Responsibility (Section 2 Homicide Act 1957)

Homicide Act 1957, s.2

  • Indictable only
  • Life imprisonment

Definition

A person ("D") who kills or is a party to the killing of another is not to be convicted of murder if D was suffering from an abnormality of mental functioning which (a) arose from a recognised medical condition, (b) substantially impaired D's ability to do one or more of the things mentioned in subsection (1A), and (c) provides an explanation for D's acts and omissions in doing or being a party to the killing. (Homicide Act 1957, s.2(1)) Those things are (a) to understand the nature of D's conduct; (b) to form a rational judgment; (c) to exercise self-control. (Homicide Act 1957, s.2(1A)) A person who but for this section would be liable, whether as principal or as accessory, to be convicted of murder shall be liable instead to be convicted of manslaughter. (Homicide Act 1957, s.2(3))

Points to prove

  1. All of the elements to prove murder are present, including an intention to cause death or grievous bodily harm
  2. and the defendant proves (s.2(2)) that the defendant was suffering from an abnormality of mental functioning
  3. which arose from a recognised medical condition
  4. which substantially impaired the defendant's ability to understand the nature of their conduct, or to form a rational judgment, or to exercise self-control (or any combination)
  5. and which provides an explanation for the defendant's acts and omissions in doing or being a party to the killing

Manslaughter by reason of diminished responsibility is the conviction that results where the partial defence in s.2 Homicide Act 1957 applies to a charge of murder. A person ("D") who kills or is a party to the killing of another is not to be convicted of murder if D was suffering from an abnormality of mental functioning which arose from a recognised medical condition, substantially impaired D's ability to understand the nature of D's conduct, to form a rational judgment or to exercise self-control, and provides an explanation for D's acts and omissions in doing or being a party to the killing (s.2(1) and (1A)). An abnormality of 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 (s.2(1B)). On a charge of murder it is for the defence to prove that the person charged is by virtue of the section not liable to be convicted of murder (s.2(2)), and a person who but for the section would be liable to be convicted of murder shall be liable instead to be convicted of manslaughter (s.2(3)). The CPS guidance lists the four elements the defendant must prove and notes that the onus is on the defendant on the balance of probabilities (CPS legal guidance, Homicide: Murder, manslaughter, infanticide and causing or allowing the death or serious injury of a child or vulnerable adult). Maximum sentence: whosoever shall be convicted of manslaughter shall be liable, at the discretion of the court, to be kept in penal servitude for life (Offences against the Person Act 1861, s.5, as the text reads with words repealed); the CPS guidance gives manslaughter as carrying sentences up to a maximum of life imprisonment.

In practice

This is an indictable-only offence: it must be tried at the Crown Court. The charging decision rests with the CPS (not police). Officers should photograph injuries at the earliest opportunity and again after 24-48 hours (bruising develops). Domestic abuse cases require completion of a DASH risk assessment. The suspect must be cautioned in accordance with Code C PACE 1984 before any questions about the offence are put to them. Interviews must be audio-recorded (Code E) or, for indictable offences, may be visually recorded (Code F).

Last updated 20 October 2026. Reviewed 20 October 2026