In the criminal law of England and Wales, for a defendant to be found guilty of a result crime, the prosecution must prove a causal link between the defendant’s conduct and the prohibited consequence. Result crimes are offences where a specific outcome is a necessary element of the actus reus, such as death in murder or grievous bodily harm in offences against the person. As Allen and Edwards (2019) note, without the occurrence of the prohibited result, the crime has not been committed, though an attempt may have been. Therefore, the doctrine of causation acts as a crucial link, ensuring that liability is only attached where the defendant can be fairly said to have caused the outcome. This is established through a two-stage test, requiring proof of both factual and legal causation, which will be the focus of this essay.
Factual Causation
The first stage of the test is to establish factual causation. This is determined using the 'but for' test: would the result have occurred as and when it did, but for the defendant’s conduct? If the answer is no, then the defendant is a factual cause. If the result would have occurred anyway, independent of the defendant’s actions, then there is no factual causation and therefore no liability for the completed offence. The classic authority for this principle is R v White [1910] 2 KB 124. In this case, the defendant put poison in his mother's drink, intending to kill her. However, she died from a heart attack before consuming the poison. The court found that ‘but for’ his actions, she would have died anyway, exactly as and when she did. Consequently, he was not the factual cause of her death and could not be convicted of murder, though he was liable for attempted murder.
The 'but for' test provides a basic minimum for establishing causation, but it is very wide. As the Supreme Court confirmed in R v Hughes [2013] UKSC 56, factual causation alone is not sufficient for criminal liability. In that case, the defendant was driving without a full license or insurance, but his driving was otherwise faultless. A collision occurred which was entirely the fault of the other driver, V, who was killed. The Supreme Court held that despite being a 'but for' cause of the death (as the collision would not have happened had he not been on the road), the defendant could not be guilty of causing death by driving. There had to be something blameworthy in the manner of his driving which contributed to the result in a more than minimal way. This demonstrates that the law requires a second stage to narrow down the pool of factual causes to those which are legally significant.
Legal Causation
Once factual causation is established, the prosecution must also prove legal causation. This ensures that the defendant's conduct was not only a factual cause but also a legally culpable, substantial, and operative cause of the result. As described by legal commentators, this involves two key considerations: the defendant’s conduct must be blameworthy and must be a substantial and operative cause of the prohibited consequence (Cherkassky, 2021).
The first element, culpability, requires that the harm must result from the blameworthy aspect of the defendant's conduct. This principle is clearly illustrated in R v Dalloway (1847) 2 Cox CC 273. The defendant was driving a horse and cart without holding onto the reins. A child ran out in front of the cart and was killed. The court directed the jury that if they believed that even if the defendant had been holding the reins he could not have stopped the cart in time to avoid the death, they should acquit. The defendant’s culpable act was not holding the reins, but this was not what caused the death. Although he was a factual cause of the death, he was not a legal cause because his culpability was not linked to the outcome.
The second element is that the defendant’s act must be a ‘substantial and operative’ cause of the result. 'Substantial' means that the cause must be more than minimal, or ‘de minimis’. It does not have to be the sole or even the main cause, as long as it is a significant contributing factor. In R v Cato [1976] 1 WLR 110, the defendant injected the victim with heroin, and the victim died. The defendant's contribution was held to be a substantial cause of death, even though the victim had consented. The cause must also be 'operative', meaning that it must still be a significant factor at the time the result occurs. If a later event renders the defendant's initial act insignificant, the chain of causation may be broken.
Breaking the Chain of Causation: Novus Actus Interveniens
A defendant who is a factual and legal cause of a result may still avoid liability if the chain of causation is broken by a subsequent event, known as a novus actus interveniens. This can be an act of a third party, an act of the victim, or a natural event, but it must be sufficiently independent of the defendant’s conduct and serious enough to render the defendant’s original act no longer a substantial and operative cause.
An act of the victim themselves can break the chain of causation, but only if it is a "free, deliberate, and informed" act of a responsible adult. This principle was clarified by the House of Lords in R v Kennedy (No. 2) [2007] UKHL 38. The defendant supplied a syringe of heroin to the victim, who then self-injected and died. The court held that the victim’s voluntary and informed act of self-injection was a novus actus interveniens which broke the chain of causation, quashing the defendant's manslaughter conviction. However, this principle does not apply where the victim's actions are not truly free. In R v Field [2021] EWCA Crim 380, the defendant had manipulated and deceived the victim into drinking alcohol, leading to his death. The court held that the victim's act was not "free, voluntary and informed" as he had been duped by someone with murderous intent, and so the chain of causation was not broken.
Third-party interventions are governed by a similar principle. For a third party’s act to break the chain of causation, it must generally be free, deliberate and informed, and not a foreseeable or reasonable reaction to the situation created by the defendant. In R v Pagett (1983) 76 Cr App R 279, the defendant used his pregnant girlfriend as a human shield while shooting at police officers. The police returned fire in self-defence, killing the girlfriend. The court held that the police officers’ actions did not break the chain of causation as their conduct was a reasonable and foreseeable response to being fired upon.
In cases of medical treatment that contributes to a victim's death, the courts have set a very high bar for this to be considered a novus actus interveniens. The case of R v Smith [1959] 2 QB 35 established that if the original wound is still an ‘operating and substantial’ cause of death, then the chain is not broken, even if negligent medical treatment was also a cause. This was affirmed in R v Cheshire [1991] 1 WLR 844, where the court stated that medical negligence would only break the chain of causation if it was so independent of the defendant's acts and so potent in causing death that the defendant’s contribution was rendered insignificant. Only in very rare cases, such as R v Jordan (1956) 40 Cr App R 152, where the treatment was described as "palpably wrong" and the original wound had largely healed, has medical treatment been held to break the chain.
Finally, the law does not allow a defendant to be excused simply because the victim had an unusual vulnerability. The 'thin skull rule' dictates that the defendant must take their victim as they find them. In R v Blaue [1975] 1 WLR 1411, a victim of a stabbing refused a blood transfusion because she was a Jehovah's Witness, and subsequently died. The defendant argued that her refusal was unreasonable and broke the chain of causation. The Court of Appeal rejected this, holding that the defendant must take the whole victim, including their physical, psychological, and religious characteristics.
Conclusion
In conclusion, causation is a fundamental component of criminal liability for result crimes, ensuring that blame is attributed fairly. The legal framework requires the prosecution to navigate a two-stage process. First, the broad 'but for' test establishes a factual link. Second, the principles of legal causation narrow the scope of liability, requiring that the defendant's culpable act was a substantial and operative cause of the result. This second stage involves complex rules concerning intervening acts, which seek to determine whether the defendant's original wrongful act was superseded by a subsequent event. While doctrines such as the thin skull rule may appear harsh, they reflect a policy choice to protect the vulnerable. Overall, the law of causation, through its various tests and principles, attempts to draw a line between factual involvement and legal responsibility, a task which is essential for achieving justice in criminal law.
References
Allen, M. and Edwards, I. (2019) Criminal Law. 15th edn. Oxford: Oxford University Press.
Cherkassky, L. (2021) Criminal Law. London: Palgrave.
R v Blaue [1975] 1 WLR 1411.
R v Cato [1976] 1 WLR 110.
R v Cheshire [1991] 1 WLR 844.
R v Dalloway (1847) 2 Cox CC 273.
R v Field [2021] EWCA Crim 380.
R v Hughes [2013] UKSC 56.
R v Jordan (1956) 40 Cr App R 152.
R v Kennedy (No. 2) [2007] UKHL 38.
R v Pagett (1983) 76 Cr App R 279.
R v Smith [1959] 2 QB 35.
R v White [1910] 2 KB 124.
