Core principles of criminal liability - Partial defences

Learning Outcomes

After studying this article, you will be able to explain the main partial defences to criminal liability: loss of control and diminished responsibility. You will understand when and how each partial defence applies, how they affect liability for murder, and how to distinguish them from complete defences. You will also be able to advise clients whether a partial defence can reduce liability from murder to manslaughter in SQE2-style problems.

SQE2 Syllabus

For SQE2, you are required to understand the practical operation and consequences of partial defences to criminal liability, especially in the context of homicide. In preparation for the exam, ensure you are confident in:

• the definition and key legal elements of loss of control
• the definition and key legal elements of diminished responsibility
• the effect of each partial defence on criminal liability for murder
• the differences and overlaps between partial and complete defences in criminal law
• the burden and standard of proof for partial defences

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which two partial defences can reduce a charge of murder to voluntary manslaughter?
2. What are the three core requirements for the defence of loss of control?
3. Who bears the burden of proof in establishing diminished responsibility, and to what standard?
4. True or false? The partial defence of loss of control requires the loss to be sudden.

Introduction

When advising clients or preparing for the SQE2 exam, it is essential to understand partial defences—specifically, loss of control and diminished responsibility. These partial defences do not provide a full acquittal but can reduce liability for murder to voluntary manslaughter, affecting both sentencing and criminal records. This article explains the core requirements of each partial defence and the legal and practical consequences of raising them.

Loss of Control

The partial defence of loss of control allows a defendant charged with murder to have their liability reduced to voluntary manslaughter if strict statutory criteria are met.

Key Term: loss of control
A statutory partial defence to murder, available if the defendant lost self-control due to a qualifying trigger and an objective person might have acted similarly.

Loss of control was introduced to replace the old defence of provocation and is governed by s 54 and s 55 of the Coroners and Justice Act 2009. Loss of control can only be pleaded in response to a charge of murder.

To establish this partial defence, the following must be shown:

1. The defendant must have lost self-control. This means a loss of the ability to act with considered judgment or normal powers of reasoning. There is no requirement that the loss must be sudden, but greater delay makes its success less likely.
2. The loss of self-control must result from a qualifying trigger. There are two possible triggers:
   • Fear of serious violence from the victim against the defendant or another identified person.
   • Things said or done of an extremely grave character causing the defendant to have a justifiable sense of being seriously wronged.
3. A person of the defendant's sex and age, with a normal degree of tolerance and self-restraint and in the defendant's circumstances, might have reacted as the defendant did. This is an objective test.

There are important exclusions:

• If the loss of control was induced by a considered desire for revenge, the defence will fail.
• Sexual infidelity cannot by itself be a qualifying trigger (but may be part of the overall context).
• The defendant cannot rely on a trigger they incited for the purpose of providing an excuse for violence.

Key Term: qualifying trigger
A reason for the loss of self-control that meets strict statutory definitions: fear of serious violence, or things done/said of extremely grave character causing justifiable sense of being seriously wronged.

Worked Example 1.1

Case study: Sarah endured years of domestic abuse from her partner. After a particularly humiliating and threatening incident, Sarah snapped and fatally stabbed her partner the next day. Does the defence of loss of control apply?

Answer:
The delayed response does not itself prevent the loss of control defence. If Sarah's actions resulted from a loss of self-control attributable to fear of serious violence or things said/done of extremely grave character, and a person in her circumstances might have acted similarly, the defence may be raised. The jury would consider if she lost self-control, identify a qualifying trigger, and apply the objective test.

Exam Warning

For SQE2, remember that loss of control requires a qualifying trigger and an objective element; motive alone (e.g. anger, embarrassment) is not sufficient. The defence is only available to murder charges—never to manslaughter or other offences.

Diminished Responsibility

Diminished responsibility is a statutory partial defence to murder under s 2 of the Homicide Act 1957 (as amended). If successful, it reduces liability from murder to voluntary manslaughter.

Key Term: diminished responsibility
A partial defence to murder available if the defendant was suffering an abnormality of mental functioning that substantially impaired their responsibility for the killing, arising from a recognised medical condition.

To establish diminished responsibility, the defendant must prove:

1. They were suffering from an abnormality of mental functioning.
2. The abnormality arose from a recognised medical condition.
3. The abnormality substantially impaired the defendant's ability to:
   • understand the nature of their conduct,
   • form a rational judgment, or
   • exercise self-control.
4. The abnormality was a significant cause of the defendant's conduct in killing the victim.

Key Term: recognised medical condition
Any medical or psychiatric disorder accepted by the courts or medical profession, including mental illness, some personality disorders, intellectual disability, and some physical conditions like epilepsy.

The burden is on the defence to establish diminished responsibility on the balance of probabilities. If successful, the defendant is convicted of voluntary manslaughter rather than murder, allowing the judge discretion in sentencing.

Worked Example 1.2

Scenario: James is charged with murder after killing his business partner. At trial, expert evidence shows James suffers from severe depression and at the time of the act was unable to form rational judgments. Can James plead diminished responsibility?

Answer:
If the court accepts that James was suffering from an abnormality of mental functioning (severe depression) that arose from a recognised medical condition and that his ability to form rational judgment was substantially impaired, and this was a significant cause of the killing, James may successfully plead diminished responsibility.

Exam Warning – Diminished Responsibility

The partial defence of diminished responsibility only applies to murder. The defendant must call medical evidence to support the existence and effects of the recognised medical condition at the time of the crime.

How Partial Defences Affect Criminal Liability

Partial defences do not provide a complete acquittal. If proven, they reduce murder to voluntary manslaughter. This can significantly affect sentencing, since the mandatory life sentence for murder does not apply to manslaughter. The judge has discretion in sentencing, and a wide range of sentences may be available.

Key Term: voluntary manslaughter
An offence where all elements of murder are present but the defendant successfully raises a partial defence such as loss of control or diminished responsibility.

Worked Example 1.3

Scenario: Amal is convicted of murder after raising the defence of diminished responsibility. The jury is satisfied on the balance of probabilities. What is the effect on sentencing?

Answer:
Amal is convicted of voluntary manslaughter, and the sentencing judge now has full discretion. There is no requirement for a mandatory life sentence. Amal may receive a determinate sentence, a hospital order, or another outcome appropriate to the circumstances.

Revision Tip

For the SQE2 exam, always set out whether the evidence could satisfy the elements of loss of control or diminished responsibility. Apply each statutory element separately, and check who has the burden of proof and to what standard.

Summary

Key Point Checklist

This article has covered the following key knowledge points:

• Loss of control and diminished responsibility are partial defences to murder only.
• Loss of control requires proof of a loss of self-control, a qualifying trigger, and that an objective person might have acted similarly.
• Diminished responsibility requires an abnormality of mental functioning from a recognised medical condition that substantially impaired responsibility for the killing.
• Both partial defences, if successfully raised, reduce liability from murder to voluntary manslaughter, avoiding a mandatory life sentence.
• The defence has the burden of proving diminished responsibility on the balance of probabilities; for loss of control, the defence must raise evidence and the prosecution must disprove it.
• Voluntary manslaughter allows the judge discretion in sentencing.

Key Terms and Concepts

• loss of control
• qualifying trigger
• diminished responsibility
• recognised medical condition
• voluntary manslaughter