Revise Actus reus for Cambridge 9084 (2.1.1)

The actus reus, Latin for 'guilty act', is the external or physical element of a crime. It represents the conduct that the law seeks to prohibit. For a criminal offence to be established, the prosecution must prove beyond reasonable doubt that the defendant (D) performed the actus reus while possessing the required mens rea (guilty mind). The actus reus can take three forms: a positive voluntary act (a 'commission'), a failure to act (an 'omission') where a duty to act exists, or, in rare cases, a 'state of affairs' (e.g., being found drunk on a highway under certain statutes). Understanding this foundational component is crucial, as without a proven actus reus, there can be no crime, regardless of the defendant's intentions.

A core principle of actus reus is that the conduct must be voluntary. This means the defendant must have conscious control over their actions. If an act is involuntary, the defendant cannot be held criminally liable. The classic example of involuntary conduct is automatism, where the defendant's mind has no control over the body's movements, such as during a seizure or when being attacked by a swarm of bees while driving, as hypothesised in Hill v Baxter [1958]. Lord Denning in Bratty v AG for Northern Ireland [1963] defined automatism as 'an act which is done by the muscles without any control by the mind'. Therefore, if the prosecution cannot prove the defendant's act was voluntary, the actus reus is not established.

Generally, English law does not impose criminal liability for failing to act, as there is no 'Good Samaritan' law. However, the law recognises exceptions where a legal duty to act exists. Failure to fulfil this duty can constitute the actus reus of a crime. Such duties can arise from statute (e.g., failing to provide a breath sample under the Road Traffic Act 1988), a contract (R v Pittwood), a special relationship like parent-child (R v Gibbins and Proctor), voluntary assumption of care (R v Stone and Dobinson), or from creating a dangerous situation and failing to mitigate it (R v Miller). In these circumstances, the omission is treated as legally equivalent to a positive act, satisfying the actus reus requirement.

For result crimes, such as murder or criminal damage, the prosecution must prove that the defendant's conduct caused the prohibited consequence. This involves a two-stage test. First, factual causation is established using the 'but for' test: 'but for' the defendant's actions, would the result have occurred? If the answer is no, factual causation is proven, as seen in R v White [1910]. Second, legal causation must be shown. This requires proving the defendant's act was an 'operating and substantial' cause of the result (R v Smith [1959]). The cause need not be the sole cause, but it must be more than minimal or trivial (R v Kimsey [1996]). Both factual and legal causation must be satisfied to establish the chain of causation.

The chain of causation can be broken by a 'novus actus interveniens' – a new intervening act. This can be an act of a third party, the victim, or in some cases, medical negligence. For an act of the victim to break the chain, it must be 'so daft' or unforeseeable as to be unreasonable (R v Roberts). Medical treatment will only break the chain if it is 'palpably wrong' and so independent of the defendant's act that the original injury is merely part of the history (R v Cheshire). Importantly, the 'thin skull rule' dictates that the defendant must take their victim as they find them (R v Blaue). This means a victim's pre-existing vulnerability, whether physical, mental, or religious, will not break the chain of causation.

For a crime to be committed, the actus reus and the mens rea must coincide in time. This is known as the contemporaneity principle, or concurrence. However, the courts have developed flexible approaches to situations where the two elements appear to be separate. In cases involving a 'continuing act', the mens rea can be superimposed onto an existing actus reus, as occurred in Fagan v MPC [1969], where the intention to remain on the officer's foot was formed after the initial, accidental act. Alternatively, the 'transaction theory' allows a series of acts to be treated as one single transaction. If the mens rea exists at any point during that transaction, it is sufficient, as established in Thabo Meli v R [1954].