H418/01 - Factual and legal causation

The factual connection

Factual causation asks whether the defendant's conduct made a difference to the prohibited result.

The usual but-for test asks: but for the relevant conduct, would the result have occurred when and as it did? If it would have occurred in the same way anyway, the conduct is not a factual cause of that result. Use evidence about the actual mechanism. A sequence of “first this, then that” does not prove a causal connection, and an intention to cause harm does not substitute for causing it.

Original example: Arlo puts poison into Bea's drink intending to kill her, but Bea dies from an entirely independent heart attack before taking a sip. Removing the poisoning from the facts would not change that death. Arlo has not factually caused it, although attempted-offence liability is a separate question. If the poison instead accelerates death from a pre-existing illness, the fact that Bea would eventually have died is not an answer: consider the death when it occurred.

But-for reasoning can be too broad: many background conditions are necessary without attracting criminal responsibility. In R v Hughes [2013] UKSC 56, an uninsured and unlicensed driver was involved in a fatal collision caused by the other driver's extremely poor driving. Under the causing-death provision then in issue, mere presence on the road was insufficient; some fault in Hughes's driving contributing more than minimally to death was required. The Supreme Court allowed the appeal. It shows why identifying a necessary background condition does not finish legal causation, and why statutory context matters. It does not excuse careless driving that actually contributes to death.

For an omission, ask whether doing what the duty required would have prevented the result. The prosecution must prove the requisite causal link to the criminal standard. Evidence of only a lost possibility of rescue may leave a reasonable doubt; do not replace the criminal test with a civil percentage of lost chance.

An operative and substantial cause

Legal causation asks whether the factual contribution is sufficient to attribute the result to the defendant under the offence.

The conduct must remain an operating and substantial cause: a significant contribution, commonly expressed as more than minimal, rather than a mere historical setting. “Substantial” does not mean the largest cause or require a fixed percentage. There can be several legally relevant causes. The prosecution need not prove the defendant was the sole or principal cause.

Original application: Dara inflicts a serious wound; the victim's existing illness also contributes to death. If the wound accelerates death and remains a significant cause, the illness does not erase Dara's contribution. If reliable evidence instead establishes that an entirely independent cause produced death without any contribution from the wound, the conclusion changes. Explain which factual finding supports the result.

The thin-skull rule requires the defendant to take the victim as found. In R v Blaue [1975] 1 WLR 1411, a stabbing victim refused a blood transfusion on religious grounds and died. The refusal did not break the chain; the defendant could not demand a victim with different physical or religious characteristics. The wound remained causal. The rule does not dispense with proof of actual causation or prove mens rea from an unusually grave result.

This protects vulnerable victims and avoids allowing an assailant to shift responsibility onto the person harmed. It can also impose liability for unusually severe consequences beyond what the defendant expected. That is a reason to keep causation separate from the offence's fault requirements: unexpected severity is not automatically intention to cause that severity. Tort also uses causation and victim-vulnerability concepts, but civil liability and criminal guilt have different elements and standards of proof.

Medical treatment and other causes

Later treatment does not ordinarily erase the causal significance of the injury that made treatment necessary.

In R v Cheshire [1991] 1 WLR 844, the defendant shot the victim, who later died following complications associated with a tracheotomy and inadequate treatment. The Court of Appeal upheld the conviction. Negligent treatment breaks the chain only where it is so independent of the defendant's acts and so potent in causing death that the defendant's contribution becomes insignificant. The focus is the original conduct's remaining significance, not merely whether the doctors made mistakes.

R v Jordan (1956) 40 Cr App R 152 illustrates the exceptional boundary: the wound had largely healed, while palpably wrong medical treatment caused death. It is unsafe to turn that unusual decision into “medical negligence always breaks the chain”. Cheshire explains why ordinary treatment errors, and even serious ones, do not necessarily do so. The exact medical evidence matters.

Original comparison: a patient has an active life-threatening wound when a hospital fails to give prompt care. The wound may remain an operative, significant cause alongside the failure. If it has ceased to be significant and a wholly independent, extraordinarily harmful treatment is the sole significant cause of death, a break is more plausible. Saying the doctors were “negligent” leaves both questions unanswered.

Natural events can also intervene. An extraordinary, unforeseeable event may break the chain if it relegates the defendant's contribution to background history. An ordinary event that the original danger predictably exposes the victim to is less likely to do so. Do not use foreseeability alone as a universal formula: autonomous decisions and the construction of particular statutes may require different reasoning. Identify the intervening event, assess independence and causal potency, then state the conditions on your conclusion.

Victims and third-party interventions

A later human action may either continue the original danger or introduce an independent cause.

For a victim's escape, ask whether the response fell within a range of responses that could reasonably be expected in the circumstances, including the pressure of the moment. In R v Roberts (1971) 56 Cr App R 95, a passenger injured herself jumping from a moving car to escape sexual advances. The chain was not broken because the escape was a reasonably foreseeable response; a wholly disproportionate or unforeseeable reaction could have produced a different result. Do not judge a frightened victim as if choosing calmly in safety.

An instinctive, reasonable defensive response by a third party ordinarily does not break the chain. In R v Pagett (1983) 76 Cr App R 279, the defendant used a woman as a shield while firing at police. Police return fire killed her. Their reasonable response did not remove the defendant's causal responsibility. Contrast a third party making a free, deliberate and informed decision to embark on independent harmful conduct.

In R v Kennedy (No 2) [2007] UKHL 38, a fully informed adult freely injected heroin supplied by the defendant and died. The House of Lords held that supply did not cause the self-injection for unlawful-act manslaughter. The adult's autonomous act intervened. The conclusion depends on freedom, information and capacity: it does not establish the same result for coercion, deception or direct administration. Nor does it rule out a separate duty and later culpable omission after someone contributes to a life-threatening situation, as Evans illustrates.

Original application: a threatened person jumps from a low balcony onto soft ground and breaks an ankle. The height, threat and available exits inform whether escape was within a reasonable range. Change the threat to a minor insult, provide an obvious safe exit, and increase the jump to a very high roof: a break becomes a stronger argument. Neither scenario should be resolved merely by the word “jumped”.

Quick recap

First establish a factual contribution, then its legal significance. Evaluate an alleged intervention in context: original conduct can remain causal alongside vulnerability, treatment errors or reasonable protective responses.