Causation can be split into two separate tests:
1 – Factual causation.
The Court asks whether ‘but for’ the defendant’s conduct the prohibited consequences have occurred? If this question is answered in the negative, factual causation is established.
2 – Legal causation.
It must be shown that the defendant’s actions are an operative and substantial cause of the ensuing consequences. Legal causation justifies the imposition of criminal liability by finding that the defendant is culpable for the consequences which occurred as a result of his/her actions. This involves showing that the chain of events linking the defendant’s conduct and the consequences remains unbroken.
Factual causation is usually the starting point, with legal causation assessed in more complicated circumstances.
This section will first look at the elements of factual causation and then turn to the more complicated elements of legal causation.
The test for factual causation is the ‘but for’ test
R v Paggett 
This case demonstrates the application of the ‘but for’ test of causation.
R v White 
R v White illustrates circumstances where the defendant’s conduct has been successfully overtaken by an unrelated cause of death, breaking the chain of causation.
The test for legal causation is more complicated.
R v Dalloway 
The prohibited consequences must have been caused by a culpable act. If the consequences are not caused by the defendant’s culpable act, then legal causation is not made out.
R v Williams 
The requirement that the prohibited consequences must have been caused by the defendant’s culpable act does not apply to strict liability crimes.
R v Benge 
It is not necessary for the defendant’s actions to be the only cause. However, the defendant`s act must play a more than minimal part in the consequence.
R v Hart 
Where the other casual factor in the victim’s death is a natural event rather than the actions of a person, causation is usually attributed to the defendant.
Novus actus interveniens
R v Kennedy (No. 2) 
The case of R v Kennedy (No. 2) illustrates a set of circumstances where the victim’s voluntarily and informed choice was held to be a novus actus interveniens, breaking the chain of causation.
R v Roberts 
An act by the victim will not constitute a novus actus interveniens which breaks the chain between the defendant’s act and the consequences of this act, unless the victim has acted unreasonably in the circumstances.
R v Blaue 
This case is an example of a case where the Court held that the victim’s actions did not constitute a novus actus interveniens.
R v Dhaliwal 
The facts of R v Dhaliwal demonstrate the limits of causation. The Court was unable to attribute responsibility for a suicide to a defendant who had verbally abused the victim.
R v Michael 
A third party will not break the chain of causation when the third party’s actions are reasonably foreseeable and innocent.
The courts have often been faced with a scenario where an original wound caused by the defendant has been exacerbated by negligent medical treatment of the injury. However, they have often been inconsistent when deciding whether negligent medical intervention acts as a novus actus interveniens which breaks the chain of causation before the defendant’s actions and the victim’s death. On the basis of current authority, it seems that the medical intervention must be grossly negligent before it can intervene to break the original chain of causation. This section will look at the development of negligent medical intervention as a novus actus interveniens and the circumstances where it is sufficient to break the chain of causation.
R v Jordan 
In extreme circumstances where the medical intervention is grossly negligent, the chain of causation can be broken. This absolves the defendant of responsibility for the prohibited consequence.
R v Smith 
Where the original injury inflicted by the defendant remains an operating and significant cause, the defendant will still be considered a legal cause.
R v Malcherek and Steel 
The facts of R v Malcherek and Steel is an example of a case where medical professionals acted in line with normal medical practice, meaning their actions did not constitute a novus actus interveniens.
R v Cheshire 
The Court in R v Cheshire clarified when medical treatment constitutes a supervening act which breaks the chain of causation. The treatment provided must be so independent of the defendant’s act and so potent in causing the death that the jury regard the defendant’s acts as insignificant.