The Courts have had very little trouble dealing with positive act cases. Where someone does a positive act to kill another person, such as picking up a knife and stabbing your victim, it is clear this constitutes the actus reus of murder. However, the courts have had much more difficulty dealing with omissions (a failure to act) which leads to a death.
As a general rule, individuals are not under a duty to rescue in the UK . This means that there is no general duty for one person to prevent the death of another. For example, if I see someone drowning and omit to save them, this is not considered a criminal act. The position is different in France, where a duty to rescue is imposed.
The criminal law differentiates between positive conduct and omissions which result in death. It is much harder to ground a murder charge on the basis of an omission rather than a positive action, but the courts have established that some omissions can form the basis of a murder conviction.
In order for an omission to constitue the actus reas for murder, the defendant must owe a duty of care, imposed by law, to act to save the victim. It must also be shown that the defendant breached their duty of care. Such a duty will only be imposed in limited circumstances, which are illustrated in the cases below.
Examples where the defendant owes a duty of care to the victim
R v Gibbons and Proctor 
The Court held that a parent owes a duty of care towards their child.
R v Instan 
In R v Instan, the court stated clearly that an omission is capable of amounting to a killing. This case is also an example where the defendant was shown to owe a duty of care towards the victim.
R v Stone and Dobinson 
In R v Stone and Dobinson, the Court found that the defendant was under a duty to prevent the victim’s death. In particular, the Court relied on the defendant’s ‘assumption of responsibility’ to the victim.
R v Pittwood 
The case of R v Pittwood clarifies that the necessary duty of care required for an omission to constitute the actus reus of murder can stem from a contractual duty.
R v Evans 
In R v Evans (Gemma), the defendant was under a duty to act, and by failing to act was found guilty of an offence.
R v Miller 
The creation of a dangerous situation is capable of creating a duty to act to avert that situation from coming in to being. The failure of the defendant to act can then constitute the actus reus of the offence.
DPP v Santana-Bermudez 
The Court confirmed the correctness of R v Miller. This means that where the defendant creates a dangerous situation and omits to avert the consequences of his actions, he can be liable if reasonably foreseeable harm occurs.