The actus reus of an offence is the ‘guilty act’ which gives rise to liability. The actus reus is usually identified in a statute or in common law.
For example, the actus reus of murder is ‘unlawful killing’. The actus reus of fraud by misrepresentation is the making of a false representation. The actus reus describes the act that has to be proven in order for the offence to be made out.
For most crimes the actus reus requires the defendant to do something in order to incur liability. There is a general rule that there is no criminal liability for omissions – or failing to do something.
The mens rea describes the ‘guilty mind’ of a defendant.
Intention is the most culpable of all the kinds of mens rea. If you intend to do something, then your moral culpability is more pronounced than if you did something through negligence. This merely reflect that intending to do something involves a degree of agency which may be lacking when no intention to commit and offence is present.
Direct intention is the term we use to describe where a defendant intends to commit an offence.
Indirect intention is where the consequences of the actus reus are a byproduct – so not the principal purpose, of what the defendant was aiming to do.
The legal case for establishing an indirect intention is where the consequence was virtually certain to occur from the defendant’ act or omission. This is an objective test to be decided by the Court. The Court will then ask whether the defendant appreciated that the consequences were virtually certain to occur. This is a subjective test which will ask what the defendant themselves foresaw as a perceived consequence of their actions.
Recklessness involves the defendant taking an unjustified risk. Whether a risk is justified or not will depend on a number of factors including the reasons why a defendant acted as they did, what the risk was and the likely consequences.
The prosecution must also establish that the defendant had a particular state of mind when they took that risk.
Strict liability offences do not require the proof of any mens rea. They are committed solely by the carrying out of the actus reus.
You can identify a strict liability offence by reading the source of the offence: if it is in statute – does the statute contain a mens rea element? If the offence is defined in common law, then does the caselaw describe a mens rea element? If there is no mens rea element in either the statute or common law which creates the offence then it is likely to be an offence of strict liability.
Parties to an offence
A principal is the person who has carried out both he actus reus and mens rea of an offence.
The term ‘accomplice’ refers to someone who commits and offence alongside the principal. Section 8 of the Aiders and Abettors act states that ‘whosoever shall aid, abet, counsel, or procure the commission of any indictable offence, whether the same be an offence at common law or by virtue of any Act passed or to be passed, shall be liable to be tried, indicted, and punished as a principal offender. In practice, anyone who aids abets the principal is likely to be charged on the same basis as the principal offender.
The doctrine of Joint Enterprise has evolved over many decades of caselaw. The principals of Joint Enterprise, or as it is properly known, ‘Parasitic Accessory Liability’ (PAL).
In the case of R v Jogee; Ruddock v The Queen  UKSC 8; UKPC 7 the Supreme Court and the Privy Council addressed the controversial doctrine of “parasitic accessory liability” (PAL). Prior to the decision in Joggee, it was thought that if two people (D1 and D2) set out to commit crime A, and in the course of that venture D1 commits crime B, D2 would be guilty as an accessory to crime B if he had foreseen the possibility that D1 might act as he did.
The doctrine was crystallised in R v Powell; R v English  1 AC 1, which adopted the reasoning in R v Chan Wing-Siu  AC 168. The Court in R v Jogee held that Chan Wing-Siu took a wrong turn and was in error, as it equated foresight that D1 might commit crime B with intent to assist D1’s commission of crime B. The correct approach is to treat such foresight as evidence of intent to assist D1 in crime B. Although foresight may sometimes be powerful evidence of intent, it is not conclusive of it [66 & 87].
Where it is not possible to prove whether a particular defendant is a principal or accessory, it is sufficient to prove that the particular defendant participated in the crime as one or the other. 
However, note that where two people are jointly indicted for the commission of a crime and the evidence does not point to one rather than the other, and there is no evidence that they were acting in concert, the jury ought to acquit both: R v Lane and Lane (1986) 82 Cr. App. R. 5; R v Aston and Mason (1992) 94 Cr. App. R. 180. See also R v Lewis and Marshall-Gunn  EWCA Crim 1734, in which the prosecution case was put on the basis that the defendants were joint principals but not on the footing of it being a joint enterprise involving encouragement or assistance by one or the other.
Association between D2 and D1 and D2’s presence at the scene may or may not involve assistance or encouragement. Numbers often matter, as most people are bolder when supported or fortified by others . See the section below on “Participation” for a fuller discussion of association and presence.
Part 2 of the Serious Crime Act 2007 creates, at sections 44 to 46, three inchoate offences of intentionally encouraging or assisting an offence; encouraging or assisting an offence believing it will be committed; and encouraging or assisting offences believing one or more will be committed.
These offences replace the common law offence of ‘incitement’ for all offences committed after 1 October 2008. They allow people who assist another to commit an offence to be prosecuted regardless of whether the underlying substantive offence is actually committed or attempted.
Section 50 of the 2007 Act provides a defence to the offences in Part 2 where the encouragement or assistance is considered to be reasonable in the circumstances the person knew to exist or he reasonably believed to exist.
A person is guilty of attempting to commit an offence under the Criminal Attempts Act 1981 (CAA 1981), Section 1(1) if they do an act, which is more than preparatory to the commission of the offence, with the intention of committing an offence.
In each case it is a question of fact whether the accused has gone sufficiently far towards the full offence to have committed the act of the attempt. If the accused has passed the preparatory stage, the offence of attempt has been committed and it is no defence that they then withdrew from committing the completed offence.
When examining if the accused has passed the ‘preparatory stage,’ the approach is “to look first at the natural meaning of the statutory words” – R. v. Jones, 91 Cr.App.R. 351, CA, applying R. v. Gullefer, 91 Cr.App.R. 356, CA. It is important to consider whether the defendant had actually tried to commit the act in question or whether he had only got ready, or put himself in a position, or equipped himself to do so: R. v. Geddes  Crim.L.R. 894, CA.
The case of R v Qadir and Khan  9 Archbold News 1, CA states the following: “Attempt begins at the moment when the defendant embarks upon the crime proper, as opposed to taking steps rightly regarded as merely preparatory.”
An attempt is an offence of specific intent. It requires an intention to commit an offence to which Section 1(4) Criminal Attempts Act 1981 applies.
Although summary offences cannot be the object of a criminal attempt under Section 1 of the CAA 1981, provisions creating summary offences sometimes create matching offences of attempt. Sections 4 and 5 of the Road Traffic Act 1988, for example, create summary offences of driving or attempting to drive when unfit through drink or drugs or when over the prescribed limit for alcohol.