The defence of diminished responsibility, like the defence of provocation, was introduced in the Homicide Act 1957 and is contained in s2(1).
Diminshed responsibility is a partial defence to murder based upon recognition of a recognised medical condition that if successful, results in verdict of voluntary manslaughter that does not carry a mandatory life sentence.
When the area of voluntary manslaughter was subject reform by the Coroners and Justice Act 2009,the defence was not abolished and replaced, but rather updated, the updates where outlined within s52 Coroners and Justice Act 2009.
The full citation for reference is therefore s2(1) Homicide Act 1957 as amended by the Coroners and Justice Act 2009.
Diminished responsibility like the defence of loss of control is a special and partial defence.
There are four elements of the defence, all of which must be proved in order for the defence to be available.
The first element of the defence requires the jury to determine as a question of fact, rather than medicine, whether the defendant’s state of mind at the time of killing was ‘abnormal’.
The phrase under the the Homicide Act 1957 was ‘abnormality of mind’ and was updated to ‘mental functioning’ by the Coroners and Justice Act 2009, neither statute sought to define this term, we therefore must rely upon the common law definition as provided by the courts.
It has been confirmed by the courts on a number of occasions that this definition still applies to the phrase ‘abnormality of mental functioning’, despite the slight change in wording as Parliament chose not to provide a definition in the Coroners and Justice Act 2009.
Once the state of mind requirements of ‘abnormality of mental functioning’ have been proved, it must be established that the cause of this is a recognised medical condition, rather than a state of intoxication for example. The link between these two is important to establish as a basis for the defence.
The term ‘recognised medical condition’ is wide and not defined in the statute. At trial the presence of a recognised medical condition, or lack of will be supported by expert witnesses, who can be presented by both the prosecution and defence. Just because there is an accepted recognised medical condition present does not automatically mean the defence is available, the remaining elements may still remain unproved.
The CPS states the recognised medical conditions can be found in the ‘World Health Organisation's International Classification of Diseases (ICD-10) and the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)’ - https://www.cps.gov.uk/legal-guidance/homicide-murder-and-manslaughter
This term despite relating to the mind of the defendant is not limited to just psychiatric or psychological conditions but can also include physical health conditions, provided they have caused an ‘abnormality of mental functioning’.
Examples have included:
Byrne (1960): sexual psychopathy.
R v Conroy (2017): Autism Spectrum Disorder.
R v Dietschmann (2003): adjustment disorder.
R v Wood (2008): alcohol dependency syndrome.
Once it has been established that the defendant has a medical condition which has caused an abnormality, it must further be proved that the abnormality substantially impaired the defendant’s mind in one of three ways:
(a) to understand the nature of his conduct.
(b) to form a rational judgement; or
(c) to exercise self-control.
It is important to note that the abnormality must only substantially impair the defendant in one of these three ways not all of them. The three criteria are outlined within the statute.
The use of the word substantial also means that it does not have to be proved that one of the three mental abilities has been totally impaired, rather substantially.
The fourth element of the defence requires proof that the abnormality caused by the recognised medical condition, which has caused the substantial impairment has either caused or is a significant factor in causing the defendant to kill. It is important to recognise that the four elements of this defence are inherently interconnected and do not stand alone as independent tests.
This fourth element was a new requirement introduced by the Coroners and Justice Act 2009 and involves the jury making an assessment of the reasons why the defendant killed, the defence will only be available if they feel that at the time the defendant killed, the abnormality was one of the significant reasons. Therefore, it need not be proved that the abnormality of mental functioning is the only cause (reason) the defendant took part in the killing, there may be other reasons the defendant killed which do not prevent the defence from being available, however the abnormality must be a significant factor.
Section 1B Homicide Act 1957: ‘… 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’.
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