# Actus reus: the external element of criminal liability

> **Key takeaway:** Actus reus = external elements of the offence (conduct / circumstance / result + causation). Omissions: only with recognised duty (e.g. Miller; Stone and Dobinson). Causation: but-for (White) + legal cause; informed voluntary third-party intervention may break the chain (Pagett).

- **Jurisdiction:** England & Wales
- **Practice area:** Criminal
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Criminal/actus-reus
- **Keywords:** actus reus, omission, causation, R v Miller, duty to act, novus actus, criminal liability, external element

## What is this about?

Criminal liability ordinarily requires proof of the actus reus (the prohibited conduct, circumstance, or result defined by the offence) and the corresponding mens rea, unless the offence is one of strict or absolute liability. Actus reus analysis asks what the prosecution must prove as the external elements and whether those elements are satisfied by the defendant's acts or, more rarely, omissions.

## What is the core rule?

The actus reus is the external component of an offence as defined by statute or common law: conduct, surrounding circumstances, and/or a prohibited result, together with any required causal link between conduct and result. Liability for omissions arises only where the offence is capable of commission by omission and a recognised duty to act exists (e.g. statutory duty, special relationship, voluntary assumption of care, or creation of a dangerous situation). Causation in result crimes requires both factual causation (but-for) and legal causation (no novus actus interveniens breaking the chain).

## What are the elements or test?

1. Identify the statutory or common-law definition: which conduct, circumstance, and result elements must be proved?
2. Has the prosecution proved each external element to the criminal standard?
3. If a result crime: factual causation (but-for) and legal causation (operating and substantial cause; intervening acts)?
4. If omission is alleged: is there a recognised duty to act, and does the offence definition allow omission liability?
5. Consider coincidence with mens rea (continuing act / single transaction doctrines where timing is in issue)

## Which authorities matter?

- **R v Miller [1983] 2 AC 161** — House of Lords: a defendant who accidentally creates a dangerous situation may be under a duty to take reasonable steps to avert the danger; failure can supply the actus reus by omission.
- **R v White [1910] 2 KB 124** — Classic but-for causation: the defendant's act must be a factual cause of the result.
- **R v Pagett (1983) 76 Cr App R 279** — Legal causation and intervening acts: free, deliberate, informed third-party acts may break the chain; reasonable acts of self-preservation or law enforcement often will not.
- **R v Stone and Dobinson [1977] QB 354** — Duty arising from assumption of care for a vulnerable person; omission to obtain help can found manslaughter liability where the duty and gross negligence are proved.

## How does this apply in practice?

This note addresses the external element and causation/omission structure. Mens rea, strict liability classification, secondary participation, and inchoate offences are outside scope. Always start from the offence-creating provision's wording rather than generic labels.

## What are common pitfalls?

- Assuming every offence can be committed by omission without a duty and a compatible offence definition
- Stopping at but-for causation without legal causation analysis in multi-actor cases
- Conflating actus reus failure with a mens rea defence
- Overlooking that some 'status' or circumstance elements still require proof as part of the external offence

## When would a practitioner use this?

Use when analysing charging advice, half-time submissions, or appeals that turn on whether the external elements and causation were made out.

## Quick reference

Actus reus = external elements of the offence (conduct / circumstance / result + causation). Omissions: only with recognised duty (e.g. Miller; Stone and Dobinson). Causation: but-for (White) + legal cause; informed voluntary third-party intervention may break the chain (Pagett).

---

*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*