(1)In section 2 of the Homicide Act 1957 (c. 11) (persons suffering from diminished responsibility), for subsection (1) substitute—
“(1)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.
(1A)Those things are—
(a)to understand the nature of D’s conduct;
(b)to form a rational judgment;
(c)to exercise self-control.
(1B)For the purposes of subsection (1)(c), 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.”
(2)In section 6 of the Criminal Procedure (Insanity) Act 1964 (c. 84) (evidence by prosecution of insanity or diminished responsibility), in paragraph (b) for “mind” substitute “mental functioning”.
(1)Section 5 of the Criminal Justice Act (Northern Ireland) 1966 (c. 20) (effect, in cases of homicide, of impaired mental responsibility) is amended as follows.
(2)For subsection (1) substitute—
“(1)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 mental 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.
(1A)Those things are—
(a)to understand the nature of D’s conduct;
(b)to form a rational judgment;
(c)to exercise self-control.
(1B)For the purposes of subsection (1)(c), 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.
(1C)Where, but for this section, D would be liable, whether as principal or as accessory, to be convicted of murder, D is liable instead to be convicted of manslaughter.”
(3)In subsection (2), for “subsection (1)” substitute “subsection (1C)”.
(4)In subsections (4) and (5), for “mental abnormality” substitute “abnormality of mental functioning”.