Classifications of Crime
English law does not generally recognise ‘thought crime’. There needs to be some element of behaviour or physical manifestation of the defendant’s anti-social state of mind. This element of behaviour is known as the actus reus.
The prosecution is obliged to prove all elements of the actus reus before the defendant can be convicted of a crime.
The prosecution must also prove that the actus reus and mens rea coincided: the defendant must have had a ‘guilty mind’ at the time the actus reus was being carried out: Criminal Injuries Compensation Authority v First-tier Tribunal  EWCA Civ 1554.
Types of Actus Reus
There are four main types of actus reus:
- Conduct crimes: where the actus reus is the performance of a particular kind of behaviour.
- Result crimes: where the actus reus is causing some kind of proscribed result.
- State of affairs crimes: where the actus reus involves the person existing in a defined state of affairs.
- Crime of omission: where the actus reus is the failure to act or prevent a particular result/state of affairs.
Many crimes encompass multiple kinds of actus reus. For example, murder is both a conduct crime and a result crime. The defendant must do an act which causes death. Rape, meanwhile, is a conduct crime because the defendant must penetrate the victim’s vagina, mouth or anus with their penis. It is also a state of affairs crime because the victim must not be consenting.
Crimes of Omission
The General Rule
As a general rule, there is no liability for failing to act in English law. There is often an exception where the defendant was under a pre-existing duty to act to prevent the harm.
Which Offences Can be Committed by Omission?
Offences of Omission: some offences are worded in terms of omissions, such as the offence failing to provide a police officer a breach sample when obliged to do so.
Offences Against the Person: battery and assault cannot be committed by omission (save where the defendant has created a dangerous situation, see below): Innes v Wylie (1844) 1 Car & Kir 257. There does not appear to be any such limit to the other offences.
Statutory Offences: whether a statutory offence can be committed by omission depends on its construction. In practice, the courts tend to interpret statutes as including omissions unless it specifies that the defendant must ‘do acts’ or something similar: R v Ahmad (1986) 84 Cr App R 64.
Which Defendants Owe a Duty to Act?
Assuming the offence can be committed by omission in theory, the prosecution must prove that the defendant owed a duty to act. The following are the recognised category of duty:
People with a family relation to a vulnerable or dependent individual, such as a child or ill person, tend to owe them a duty to prevent harm: R v Hood  EWCA Crim 2772; R v Instan  1 QB 450.
Assumption of Responsibility
Any person who has voluntarily undertaken to protect or look after a person is under a duty to keep them safe from harm. Other behaviour may involve an assumption of responsibility for the safety of others, such as storing dangerous material or engaging in a particular business activity: Winter and Winter  EWCA 1474.
A person who has a duty to act under contract may be criminally liable even when people who are not a party to the contract are harmed as a result of inaction: R v Pittwood (1902) 19 TLR 37.
If the defendant does something which imperils others and is aware of the potential danger, he comes under a duty to take reasonable steps to prevent others from being injured by that danger: R v Miller  2 AC 161.
Distinguishing Acts from Omissions
In some cases, the defendant’s behaviour might be characterised as both an act or an omission. This is most common in medical termination of life cases. When a doctor turns of a life support machine, are they omitting to treat or actively ending the patient’s life? In medical cases, the courts are usually inclined to treat the cessation of treatment as an omission even when it involves positive acts (such as unplugging a life support machine): Airedale National Health Service Trust v Bland  AC 789.
The distinction may turn on what kills the patient. If they are allowed to die of natural causes, their underlying disease or some other circumstance the defendant did not create, this is treated as an omission. If the intervention directly kills the patient (e.g. administering lethal drug), this is normally treated as a positive act.