FLK2 · Criminal Liability

Causation in crime

SQE1 revision notes — the key rules, leading cases and common traps for this topic, in plain English and current to 2026.

CRL.02 — Causation in Crime

For any result crime (e.g. murder, manslaughter, s.18/s.20 OAPA 1861, criminal damage), the prosecution must prove the defendant's conduct caused the prohibited result. Causation splits into factual and legal causation; both must be satisfied.

Factual causation — the "but for" test

But for D's conduct, would the result have occurred? If it would have happened anyway, factual causation fails. R v White [1910] (son poisoned mother's drink; she died of an unrelated heart attack first — no factual cause; convicted only of attempt). This is a necessary minimum, not enough on its own.

Legal causation — D's act must be a substantial and operating cause

More than minimal/de minimis: the contribution must be substantial (not trivial) — R v Hughes [2013] clarifies it need not be the sole or main cause, but must be more than negligible.
Operating cause: D's act must still be operating at the time of death — R v Smith [1959] (stab wound still the operating and substantial cause despite poor medical treatment).

The thin-skull rule

Take your victim as you find them — physical, psychological, and religious/belief characteristics. R v Blaue [1975] (Jehovah's Witness refused a blood transfusion; refusal did not break the chain).

Intervening acts (novus actus interveniens) — chain-breakers

Medical treatment: rarely breaks the chain. Only if treatment is "so independent of D's acts and so potent in causing death" that the original wound is merely the setting — R v Cheshire [1991]; contrast R v Jordan [1956] ("palpably wrong" treatment, wound healed).
Victim's own act: breaks the chain only if free, deliberate and informed, or if D's escape-prompting conduct made the victim's reaction not "daft"/disproportionate — R v Roberts [1971]; R v Williams & Davis [1992].
Drug supply: the victim's free, voluntary self-injection breaks the chain — R v Kennedy (No 2) [2007].
Third party acts: break the chain only if free, deliberate and informed and not foreseeable.

Common traps

"But for" alone is never sufficient — always go on to legal causation.
Bad medical treatment almost never breaks the chain (Cheshire is the rule, Jordan the rare exception).
D need not be the only cause; substantial-and-operating suffices.
Thin-skull covers beliefs, not just physical frailty (Blaue).
Self-injection (Kennedy) breaks the chain; mere supply does not cause death.

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