3.2 - Necessity defences

The Defence Map

Necessity defences ask whether D should avoid criminal liability because the offence occurred under urgent pressure. The three AQA topics do not all work in the same way.

The first distinction is between a justification and an excuse.

Self-defence usually says the law permits D's force because it responded to unlawful danger. Duress usually says D's conduct remains wrong, but D should not be blamed because the pressure was extreme. That difference matters for evaluation: self-defence is closer to public protection and autonomy, while duress is closer to fault, compassion and policy limits.

The second distinction is force and offence under pressure. Self-defence concerns force used against a person. Duress may apply to many offences committed because of a threat or danger, but it is not a general permission to choose any lesser evil. AQA scenario answers should therefore begin by naming the defence that actually fits the facts.

Use this first-issue check:

Once the correct defence is selected, the legal method is similar: state the test, identify the authority, apply only material facts, and conclude with a calibrated outcome. The most important material facts are the seriousness of the danger, D's belief, whether the response was necessary, whether the response was proportionate, and whether D had a realistic legal alternative.

Self-Defence And Necessity

Self-defence/prevention of crime is a complete defence where D uses lawful force to protect self, protect another or prevent crime. It is partly common law and partly statutory. For AQA, the key statutory sources are Criminal Law Act 1967 s3(1), which permits reasonable force in the prevention of crime or lawful arrest, and Criminal Justice and Immigration Act 2008 s76, which sets out principles for assessing self-defence and related force defences.

The defence has two main questions:

1. Necessity: Did D honestly believe that using force was necessary?
2. Reasonableness of force: Was the degree of force reasonable in the circumstances as D believed them to be?

The necessity question is based on D's honest belief. In R v Williams (Gladstone), D's mistaken belief could support self-defence if it was honestly held. Section 76 CJIA 2008 reflects the same basic approach: D is judged on the circumstances as D believed them to be. The belief does not have to be reasonable before it can be considered, but unreasonable beliefs are less likely to be accepted as genuinely held. Under s76(5), D cannot rely on a mistaken belief attributable to voluntarily induced intoxication. For statutory prevention of crime under s3, a crime must actually be occurring or have occurred; an honest mistake can instead raise the relevant common-law self-defence analysis.

Necessity can arise before D is actually hit. In Beckford v The Queen, the law recognised that a person who honestly believes an attack is imminent does not have to wait to be struck before using defensive force. This is why a pre-emptive strike may be lawful if the facts support an honest belief in imminent danger.

There is no absolute duty to retreat. R v Bird is useful because it shows that D does not have to demonstrate unwillingness to fight as a legal requirement. However, possible retreat still matters as evidence. If D had a clear, safe chance to walk away, call for help or close a door, a court may doubt that force was necessary. If retreat would expose D or another person to real danger, the defence becomes stronger.

Use this operational test:

Example: D sees V swing a heavy chair towards D's friend. D pushes V away before the chair lands. Necessity is strong because D honestly believes force is needed to protect another from immediate injury. If D instead follows V into another room several minutes later and punches V after the danger has ended, necessity is weak because the force looks retaliatory.

Reasonable Force And Limits

Even if some force was necessary, the degree of force must still have been reasonable. Once self-defence is sufficiently raised, the prosecution must disprove it beyond reasonable doubt. This is the proportionality stage. The question is not whether D acted perfectly, but whether D's response was legally reasonable in the circumstances as D believed them.

Section 76 CJIA 2008 recognises that people acting in emergencies cannot weigh their force with perfect precision. That helps D where the response is instinctive and broadly proportionate. It does not allow unlimited violence. In ordinary cases, disproportionate force will not be reasonable. In householder cases, the statutory approach gives some extra latitude against intruders, but grossly disproportionate force will still not be reasonable; force below that threshold is not automatically reasonable and the jury must still assess all the circumstances. AQA evaluation has specifically treated homeowners, proportionality and mistaken force as important issues, so avoid writing that homeowners may do "anything" to an intruder.

The leading warning case is R v Clegg. Once D's force is excessive, self-defence fails completely. There is no partial self-defence verdict in ordinary offences: if the force is not reasonable, the defence does not reduce liability merely because D was initially under threat.

Reasonable force depends on the facts:

Be careful with the word proportionate. It does not mean equal force. A smaller person may use a weapon against a stronger armed attacker if that is reasonably necessary. It also does not mean D can escalate without limit. The exam skill is to explain why the particular response is above or below the legal threshold.

Change one fact: if D strikes V repeatedly after V has dropped the knife and is lying still, the initial strike may be justified but the later blows are likely excessive. Self-defence may fail for those later acts.

Duress By Threats

Duress by threats is a common-law excuse. D accepts that the offence was committed but argues that threats of death or serious injury left D with no fair opportunity to choose lawful conduct. If properly raised, the prosecution must disprove it. If successful, it is a complete defence and leads to acquittal. AQA assessment material also emphasises that duress is not available for murder or attempted murder.

The core elements are:

The threat must be serious. AQA has tested the point that duress is not available where D acts because of a serious threat to reputation. The threat must be death or serious injury. It can be one of several pressures: R v Valderrama-Vega is useful because threats of violence were considered alongside other pressures, and the existence of other pressures did not automatically prevent duress if a qualifying threat operated on D.

Graham first asks whether D reasonably believed the threat of death or serious injury and whether it caused the offence. This differs from the honest-belief rule for self-defence. The objective stage then asks whether a sober person of reasonable firmness sharing legally relevant characteristics would have responded similarly.

The objective stage prevents the defence becoming purely subjective. The question is not simply "Was D frightened?" but whether a person of reasonable firmness, sharing relevant characteristics such as age or sex where appropriate, might have responded in the same way. Characteristics are not used to make cowardice reasonable; they are used where they affect D's ability to resist the threat in a legally relevant way.

Escape routes are central. If D had time and safety to go to the police, leave the area or avoid the offence, duress weakens. Hudson and Taylor is usually used to show that the law can recognise continuing threats where police protection is not realistically effective. But the more realistic and safe the alternative, the more likely the defence fails.