Causation — SQE1 FLK1 Tort Law

Three night watchmen drink tea. The tea has arsenic in it. All three walk into a hospital casualty department, and the receptionist sends them home without a doctor ever seeing them. One of them, Mr Barnett, later dies of arsenic poisoning. The hospital was careless. Nobody disputes that. Was it liable for his death? No. Not a penny.

That is causation. It is the link between the breach of duty and the damage, and it is a separate hurdle. Prove duty. Prove breach. You still have to show the negligence actually caused the harm, and then that the defendant should answer for it in law. This is Causation, the third topic in Tort Law. Keep Mr Barnett in mind. He comes back.

Here is the route. Factual causation first: the but-for test, and what the courts do when it fails. Then legal causation, where the question becomes remoteness. Then the intervening act, in its four forms: doctors, the claimant, third parties, and nature. Then multiple causes, and asbestos. And last, the eggshell skull.

Start with fact. The but-for test asks one question. But for the defendant's negligence, would the claimant have suffered the harm? If the answer is yes, the harm was coming anyway, and the defendant is not a factual cause. If the answer is no, the defendant caused the damage. Take the negligence out of the story. Does the ending change?

Which is what happened to Mr Barnett. Take away the receptionist's failure to call a doctor, and he still dies. The arsenic was going to kill him regardless. So the negligence did not cause the death on the balance of probabilities, and the claim failed. That is Barnett v Chelsea and Kensington Hospital, from 1969. Breach proved. Claim lost.

Two things carry over. The burden sits on the claimant. And the standard is the balance of probabilities, which means more likely than not.

Now break the test. Suppose two separate negligent acts, and either one on its own would have caused the same harm. Ask the but-for question of the first defendant and the answer is that the harm would have happened anyway, because of the second. Ask it of the second and you get the same answer. Both walk free, which cannot be right.

One variation to hold separately. A Rolls-Royce already needed a full respray when a second driver struck the same panels, and he was not liable for it. Where an earlier event has already made a loss inevitable, a later sufficient cause adds nothing.

So what do the courts do when the test fails? Where the claimant cannot prove on the balance of probabilities that the negligence caused the harm, they may still find causation if the defendant materially contributed. A man worked for years in a foundry containing two kinds of dust. One was harmful, and the employer failed to control it. The other was harmless.

He developed a lung disease, and he could not prove which dust had caused it. The House of Lords held the employer liable anyway, because the breach had materially contributed, and material means more than negligible. Hold the distinction. The but-for test asks whether this caused the harm. Material contribution asks whether this contributed. It is another route to the same conclusion.

Factual causation done. Now the second gate, and it catches candidates who think the work is finished. Legal causation asks whether the defendant should answer for the type of damage that actually happened, or whether it is too remote. The test is reasonable foreseeability. Was this type of damage a reasonably foreseeable consequence of the negligence?

Sydney Harbour. The defendants negligently discharge furnace oil into the water, and it drifts and fouls a wharf. Men are welding on that wharf, and molten metal sets fire to cotton waste floating in the oil. The fire destroys the wharf. Foreseeable? Oil on water was known to be difficult to ignite. So the Privy Council allowed the contamination damage and refused the fire damage. That is the Wagon Mound, from 1961.

The rule is about the type of damage, not the exact manner. It need not be foreseeable in its precise details. Post office workers once left a manhole open with a tent over it and paraffin lamps around it. A child climbed in, dropped a lamp, and the explosion burned him. Burns were a foreseeable risk of unguarded lamps. The explosion was unusual. The type of harm was not.

A second action followed from the same fire, brought by the owners of ships it destroyed. This time the evidence showed the defendants' chief engineer had known that oil on water could be ignited by molten metal. Same oil, same fire, different result. They were liable. And once the type of damage is foreseeable, the defendant answers for the full extent of it, however much worse it turns out to be.

Hold the path in your head, because the flowchart is your answer plan. Did the breach cause the damage? Run the but-for test. If it passes, move to legal causation. If it fails, ask whether there were multiple sufficient causes and whether the defendant materially contributed. Then ask whether an intervening act broke the chain. Then whether the type of damage was foreseeable. Then the eggshell skull.

The intervening act, then. Novus actus interveniens means a new act intervening. The defendant is negligent, and then something else happens that contributes to the damage. Does that new act break the chain? The general rule is that it does not. It breaks the chain only where it is so extraordinary or unreasonable that the original negligence is no longer the effective cause.

Four kinds turn up. Medical negligence, where treatment after the injury makes things worse. The claimant's own actions, where the injured person does something unreasonable. Third-party acts, where somebody else contributes. And natural events, where a storm makes an injury worse. Courts are reluctant to let a defendant escape simply because something else happened along the way.

Doctors first, and try this one. Your client's careless driving puts a woman in hospital with a broken leg. The doctor treats her negligently and she is left worse off. Has the chain broken? No. It is foreseeable that an injured person will need medical attention, and the original wrongdoer takes the consequences of that foreseeable need.

When does it break? Only where the treatment is so gross or so independent that it supersedes the original injury as the cause. A surgeon amputating the wrong limb is the illustration. Keep the two apart. Treatment that worsens an existing injury: chain intact. Entirely new and independent negligence creating a new injury: chain may break.

The claimant next. Reasonable steps to get better do not break the chain. Follow medical advice, attend physiotherapy, and the defendant stays liable. It would be unfair to punish someone for trying to recover. Unreasonable conduct is different. A man's leg had been left weaker by the defendant's negligence. Going down stairs, it gave way. Instead of holding the handrail or sitting down, he tried to jump to the bottom.

The court held that his conduct broke the chain. He could not recover for the further injury, because jumping was not a reasonable response to the injury he already had. Mind the line, though. Conduct that is unreasonable but not extraordinary does not break the chain. That is contributory negligence under the Law Reform (Contributory Negligence) Act 1945, and it reduces damages rather than defeating the claim.

Third parties now, and the instinct is the same. As a general rule their acts do not break the chain. Borstal boys escaped from a detention centre on an island because the Home Office supervised them negligently. They boarded a yacht, drifted it out to sea and caused damage. The House of Lords held that their actions did not break the chain. Unsupervised young offenders causing mischief was entirely foreseeable.

So when does a third party break it? Only where the act is free, deliberate and informed. Voluntary, with full knowledge of the consequences, and not a foreseeable response to the negligence. A police officer was negligently instructed to ride a motorcycle down a closed tunnel to warn traffic, and he crashed. That choice to ride in was his own, and it broke the chain.

Contrast a council whose burst water main forced a woman out of her house. Squatters moved into the empty property and damaged it, and the council was not liable. That damage was too remote, not a very likely consequence. The threshold is deliberately high.

Nature is the fourth, and it almost never breaks the chain. Ordinary weather, tides and natural deterioration are all foreseeable. But take a ship damaged in a collision, which then took storm damage on its way to repairs. It could not recover loss of profit for the time it spent in dry dock. It had to be dry-docked for the storm anyway.

Which brings us to the hardest corner of the topic. A worker is exposed to asbestos by several employers across a working life. He develops mesothelioma, a fatal lung cancer. Nobody can say whose dust triggered it. Run the but-for test against any one employer and it fails, because the disease might have come from any of the others. On the strict rule, all of them walk away.

The House of Lords would not have that. In Fairchild v Glenhaven Funeral Services, from 2002, it held that each employer who had materially increased the risk of the disease was liable. The claimant did not have to prove which exposure did it. The House later apportioned that liability, so each defendant was liable only for a proportionate share of the risk it had created.

Parliament stepped in. Section 3 of the Compensation Act 2006 deals with mesothelioma cases where the claimant was exposed to asbestos by more than one employer. In those cases the court may hold each employer jointly and severally liable for the full damage. The claimant recovers the whole amount from any one of them. Whoever pays then seeks contribution from the others.

Last piece, and it is the one that pays. The eggshell skull rule, also called the thin skull rule. The defendant must take the claimant as they find them. If a pre-existing condition makes the claimant more vulnerable, the defendant is liable for the full extent of the damage, even where an ordinary person would have suffered far less.

A man was burned on the lip by molten metal at work. Minor burn. It would have healed on its own. But it triggered a pre-existing cancerous condition, and he died of cancer three years later. His employer argued it should pay for the burn and nothing more. The court held it liable for the death. That is Smith v Leech Brain, from 1962.

The rule has a limit, and that is where the marks are. It applies where the type of damage is foreseeable and only the severity is not. Cut someone negligently and they turn out to be a haemophiliac who bleeds to death, and you pay for the death, because bleeding is a foreseeable consequence of a cut. Minor property damage followed by an unrelated psychiatric condition is not recoverable.

And the defendant need not know about the condition. Ignorance of it is no defence. You take the claimant with whatever vulnerabilities they have.

A word on how SQE1 tests all this. You will not be asked to recall a case name or a section number. You get a scenario, five answers, and one instruction: pick the best. So learn the rules and the reasoning. The names in this episode are memory pegs, nothing more.

If you keep only three. Barnett v Chelsea and Kensington Hospital, where the hospital was careless and still paid nothing, because the man would have died anyway. The Wagon Mound, where the type of damage has to be foreseeable before anyone pays for it. And Smith v Leech Brain, where a burnt lip became a fatal cancer and the employer paid for all of it.

Four traps. One: breach is not causation. A defendant can admit the breach and still win, because the claimant has to prove that the negligence made a difference. Work both stages, factual then legal, every single time.

Two: type against extent. Ask first whether the type of damage was foreseeable. If it was not, the claim fails on remoteness. If it was, the defendant pays for the whole of it, however much worse it turned out than anyone expected.

Three: do not confuse a broken chain with contributory negligence. Truly unreasonable or reckless conduct by the claimant defeats the claim for the further damage altogether. Conduct that is merely careless reduces the damages instead. Complete defence, partial defence. Different consequences.

Four: the risk exception is narrow. It is for cases where it is genuinely impossible to identify which defendant caused the harm on the balance of probabilities. It is not a licence to skip causation, and the Compensation Act 2006 provision applies to mesothelioma. Everywhere else, the standard rules stand.

Quick check, and you have met the shape of this one. A woman is knocked down by a careless driver and taken to hospital with a fractured leg. The doctor who treats her sets the fracture badly, below the standard to be expected of him. She is left with a permanent limp that competent treatment would have avoided. She sues the driver for the whole of her disability. He says the limp is the doctor's doing, not his.

Is the driver liable for the permanent limp as well as the fracture? Three candidates. One: yes, because it is foreseeable that a person injured in a collision may be treated negligently. Two: no, because the doctor's negligence was a new act which broke the chain of causation. Three: no, because the limp would not have followed if the fracture had been set properly. Pause here if you want a moment.

The answer is one. Negligent medical treatment does not normally break the chain. It is foreseeable that a person injured by negligence will need treatment, and that the treatment may fall below standard. Only treatment so gross and egregious as to be unforeseeable severs the link. The driver stays liable for the whole of the disability.

Why the others fail. Option two treats ordinary clinical negligence as a new intervening act, and that takes something much graver. Option three shows only that the doctor was also a cause, and two negligent acts can each cause the same disability.

Five things to take away. One: run the but-for test first, and remember Mr Barnett. A hospital can be careless and still owe nothing, because the negligence made no difference. Two: where the science will not give a clean answer, material contribution can carry the claim, and in the asbestos cases each employer who materially increased the risk is liable.

Three: legal causation turns on the type of damage, not its extent and not the exact manner. Four: an intervening act rarely breaks the chain. Negligent treatment almost never does. The claimant's own conduct only when it is unreasonable. A third party only when the act is free, deliberate and informed. Five: the eggshell skull. Take your victim as you find them, and pay for the whole of it. Next time, Remoteness and Damage.

Practise this topic with exam-style questions at sqe1prep.co.uk. This episode is for education and exam revision only, not legal advice, and we are not affiliated with or endorsed by the SRA or Kaplan.