D’s act does not have to be the sole or
even the main cause, provided it is a substantial and
operating cause of death or was a significant contribution to the death (Smith;
Pagett). Substantial means that is not trifling or trivial. It does not
require proof that D’s act was largely to blame.
The act or omission must be one of the causes for example in
R v Dalloway (1847) the driver of a cart was not guilty of manslaughter
where his negligent driving did not contribute to death of child who ran into
the path of vehicle. and one that is more than minimal.
It is therefore possible to have two or more
independent operative causes of death, and any person whose conduct constitutes
a cause may be convicted of an offence in respect of the death.
The defendant's act must be more than a minimal
cause of the death. It was said by Robert Goff LJ in
"the accused's act need not be the sole cause, or even the main cause, of the
victim's death, it being enough that his act contributed significantly to that
Other causes which contribute to the death may be
the actions of others, (eg the acts of the police in
Pagett), or of the
Williams  (but see
Roberts (1971)). These
other causes do not of themselves relieve D of liability where D's act was a
substantial and operating cause.
The civil law notion of novus actus also
arises here; the chain of causation may be broken where the intervention was
“free, deliberate and informed.”
In English civil law that you must take
your victim as you find him, this principle applies in criminal law: for
example. This principle, known as the egg-shell skull rule, is not
confined to the victim's physical condition
Blaue . It is not of universal application, however, as seen in
An act which constitute a novus actus
interveniens breaking the chain of causation between D's act and the
resulting death relieves D of liability).
Rarely will the courts admit
the new act to be improper or negligent medical