Diminished Responsibility and the Criminal Law – Homicide Act & the Coroners and Justice Act

Diminished Responsibility

What is meant by Diminished Responsibility?

Diminished is one of three special defences which exist for the criminal offence of murder. The defence of diminished responsibility is set out in Section 2 of the Homicide Act 1957 as amended by the Coroners and Justice Act 2009. When the defence is successfully pleaded it has the effect of reducing a murder conviction to manslaughter.

Diminished responsibility is part of three special defences which differ from all other defences in the criminal law as they do not apply to all crimes – only applying to murder – and that they have the effect of reducing criminal liability rather than absolving the defendant from liability completely. Also contained within this three pronged group are the defences of provocation and suicide pact.

Requirements for Diminished Responsibility

Section 2 of the Homicide Act, as amended by the Coroners and Justice Act, sets out the three requirements which must be established by the defendant in order to succeed with the defence of diminished responsibility. The three requirements are as follows:

There must be an abnormality of mental functioning
This abnormality of the mind must have been caused by a recognised medical condition
The abnormality of the mind must substantially impair the defendant’s mental responsibility

Abnormality of mental functioning

Homicide Act versus Coroners and Justice Act

The previous law under the Homicide Act stated that the defendant must be suffering from an abnormality of the mind whereas the amendment made by the Coroners and Justice Act states that the defendant must be suffering from an abnormality of mental functioning.

In order to establish whether a defendant is suffering from an abnormality of the mind medical evidence will be provided in court and it will be up to the jury to decide whether the defendant is in fact suffering from that.

The medical evidence is simply opinion, albeit it given by a medical professional qualified and often specialising in that field, and the jury is not bound to follow it. Ultimately it is the final decision of the jury as to whether the defence of diminished responsibility should succeed.

The test which will be required to establish an abnormality of the mind is that by which a reasonable man would regards as abnormal. This test has a very wide meaning and includes the ability to exercise will power and control.

What would usually be considered to be an abnormality of the mind?

The following have been held to be an abnormality of the mind in cases of diminished responsibility:

Jealousy
Pre-menstrual tension
Battered woman syndrome
Epilepsy
Chronic depression

Is it enough to simply have the condition?

In order to establish an abnormality of the mind to use the defence of diminished responsibility it is not sufficient to simply have the condition. The defendant must prove that the condition was excessive when compared to that experienced by a reasonable person.

Recognised Medical Condition

Homicide Act 1957

The second condition in order to establish the defence of diminished responsibility under the original Homicide Act was that the abnormality of the mind has to be caused by an arrested or retarded development of the mind or any inherent causes or induced by disease or injury.

What does this mean?

The courts have interpreted this as meaning that the abnormality must have been caused by a source which comes from inside that person and not a factor which is said to be outside that person. Outside factors which cause the abnormality include drugs and/ or alcohol which will not be taken into account when establishing diminished responsibility.

What is the case in relation to drug addicts or alcoholics?

As drug addiction and alcoholism is seen as a medical disease then this will be taken into account if the abnormality was brought about as a result of the disease of alcoholism or drug addiction or if it is due to the long term damage caused by the intake of such substances.

What is the case in relation to prescription drugs?

In order to establish the defence of diminished responsibility the same approach will be taken as if the defendant was intoxicated by illegal drugs.

Coroners and Justice Act 2009

Under the new law specified by the Coroners and Justice Act the requirement has been simplified stating that the abnormality of the mind must have been brought on by a recognised medical condition. This means that again diseases such as alcoholism or drug addiction will be included but impairments simply due to consumption of these substances will not.

Substantially impair the defendant’s mental responsibility

Homicide Act 1957

The third aspect to establish when pleading the defence of diminished responsibility under the Homicide Act is that the abnormality must have substantially impaired the defendant’s mental responsibility.

This means that the defendant must have not fully been aware of their actions due to the mental responsibility and any evidence of planning to commit the crime will demonstrate that the defendant’s mental responsibility has not been impaired. Therefore, the defence of diminished responsibility will not apply to a premeditated attack, only a murder which happens on the spur of the moment.

Coroners and Justice Act 2009

Again the Coroners and Justice Act simplifies this third requirement by stating that the abnormality of the mind must have substantially impaired the defendant’s ability to do one of the following things:

To understand the nature of the defendants conduct
To form a rational judgement
To exercise self control

The new act then provides additional requirements in order to establish the substantially impair the defendants responsibility which provides juries with more direction on how to establish the defence.

Provides and explanation for the defendants conduct

The Coroners and Justice Act also introduces a requirement that the abnormality of mental functioning provides an explanation for the defendants conduct.

When will this provide an explanation for the conduct?

The Coroners and Justice Act qualifies this requirement by stating that this will arise if the medical condition was the reason for the defendant carrying out the act or if it was a significant contributing factor.

Diminished Responsibility on appeal

Diminished Responsibility is often a defence which will be stated on an appeal from a murder charge. However, the medical condition must have been cited in the original trial for it to be later relied on as a defence in the appeal hearing.


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Diminished Responsibility and the Criminal Law – Homicide Act & the Coroners and Justice Act