Diminished responsibility comes under s2 Homicide Act, amended by s52 Coroners and Justice Act 2009.
Diminished responsibility has 4 elements:
Abnormality of mental functioning
Caused by a recognised medical condition
This abnormality must substantially impair the defendant's ability
This must provide an explanation for D's conduct.
Medical evidence must be provided in court to prove that the defendant is suffering with a mental disorder.
It is up to the jury to decide if they agree with the evidence.
The condition names must be accepted by respected classifications by organisations like World Health Organisations.
The "recognised mental functioning" is the illness.
The "abnormality of mental functioning" is the symptoms of the illness.
Diseases like alcoholism and drug addiction are included.
Wood.
Bryne: Would a reasonable man regard the mental functioning as abnormal?
The abnormality must impair the D's ability to:
Understand the nature of his conduct
Form a rational judgement
Exercise self-control
Lloyd: Word "substantial" should be given it's everyday meaning by the jury.
If the defendant would've killed without the impairment, they would not satisfy the "explanation" element.
s2(1B) amended Homicide Act 1957: "An abnormality of mental functioning provides an explanation for D's conduct if it causes, or is a significant contributory factor is causing D is carry out that conduct"
If there is an abnormality and the D has become intoxicated, the defence may be available.