Revise Causation and remoteness of damage for Cambridge 9084 (4.1.4)

For a defendant to be liable in negligence, their breach of duty must have caused the claimant's loss. This is not a single question, but a two-stage inquiry. First, the claimant must establish 'causation in fact', which uses the 'but for' test to create a factual link between the breach and the damage. Second, the claimant must prove 'causation in law', also known as remoteness of damage. This second stage acts as a legal filter, ensuring that a defendant is not held liable for consequences that are too remote or have been broken by a new intervening act. The burden of proof for both stages rests with the claimant, who must prove on the balance of probabilities that the defendant's breach caused their loss.

The primary test for factual causation is the 'but for' test. It asks: 'but for the defendant's breach of duty, would the claimant have suffered the harm?' If the claimant would have suffered the harm regardless of the defendant's breach, then causation is not established. The leading case is Barnett v Chelsea & Kensington Hospital Management Committee, where a man died of arsenic poisoning after a hospital doctor negligently failed to examine him. However, evidence showed he would have died anyway, even with proper treatment. Therefore, 'but for' the doctor's negligence, the man would still have died, so the hospital was not liable. This test establishes the basic factual link but can be difficult to apply in cases with multiple potential causes.

The 'but for' test can lead to unjust results where there are multiple cumulative causes of harm. In such situations, the courts have developed alternative tests.

1. Material Contribution to Injury: Where it is impossible to say that the defendant's breach was the sole cause, but it can be shown to have made a 'material contribution' to the injury, the defendant will be liable. In Bonnington Castings v Wardlaw, a factory worker contracted pneumoconiosis from inhaling silica dust. Some dust was from a 'guilty' source (due to the employer's negligence) and some from an 'innocent' source. The court held that the claimant did not need to prove the 'guilty' dust was the sole cause, only that it materially contributed to his disease.

2. Material Increase in Risk: In cases of scientific uncertainty, where it's impossible to prove what caused the harm, the courts may ask if the defendant's breach materially increased the risk of the harm occurring. In McGhee v National Coal Board, a worker contracted dermatitis. The cause could have been brick dust from working in kilns (non-negligent) or from cycling home covered in dust (negligent, as employer failed to provide showers). The court held the failure to provide showers materially increased the risk of dermatitis, and this was sufficient to establish causation. This principle was famously applied in Fairchild v Glenhaven Funeral Services for multiple employers exposing a worker to asbestos.

A difficult area of causation concerns whether a claimant can sue for the 'loss of a chance' of a better outcome, particularly in medical negligence cases. The general rule is that they cannot. The claimant must prove on the balance of probabilities (i.e., more than 50% likely) that the defendant's negligence caused the adverse outcome itself, not just the loss of a chance of avoiding it.

In Hotson v East Berkshire AHA, a boy had a 75% chance of developing a permanent disability from a fall, regardless of treatment. The hospital's negligent delay in diagnosis meant the 25% chance of recovery was lost. The claim failed because he could not prove that the hospital's negligence, on the balance of probabilities, caused his disability; it was already 75% likely to happen.

This was confirmed in Gregg v Scott, where a doctor's misdiagnosis delayed cancer treatment, reducing the patient's survival chance from 42% to 25%. The House of Lords held that since his initial chance of survival was already below 50%, he could not prove the negligence caused the outcome, so his claim for the lost 17% chance failed.

Even if factual causation is proven, the chain of causation can be broken by a 'novus actus interveniens' – a new intervening act. If such an act occurs, it severs the link between the defendant's breach and the claimant's ultimate loss, relieving the defendant of liability from that point onwards. An intervening act can be an act of a third party (Knightley v Johns), an act of the claimant, or a natural event. For an act to break the chain, it must be unforeseeable and independent of the original breach. For example, in McKew v Holland, the claimant's own unreasonable action of descending a steep staircase without a handrail, knowing his leg was weak, was held to be a novus actus which broke the chain of causation.

Remoteness of damage is the final hurdle in establishing causation. It asks whether the damage suffered is too remote from the original breach for the defendant to be held liable. The modern test was established in Overseas Tankship (UK) Ltd v Morts Dock & Engineering Co Ltd (The Wagon Mound No. 1). This case overruled the old, wider test from Re Polemis. The Wagon Mound test states that a defendant is only liable for damage if the type or kind of damage was a reasonably foreseeable consequence of their breach. It is not necessary to foresee the precise way the damage occurs or its full extent, only the type of damage. In The Wagon Mound, fire damage was held not to be a foreseeable consequence of spilling furnace oil into water.

The 'thin skull' (or 'eggshell skull') rule is an important qualification to the remoteness principle. It holds that a defendant must 'take their victim as they find them'. If the type of injury is reasonably foreseeable, the defendant is liable for the full extent of that injury, even if the extent is far greater than would normally be expected due to a pre-existing vulnerability of the claimant. In Smith v Leech Brain & Co, a worker was splashed with molten metal, causing a burn to his lip. The burn was a foreseeable injury. However, the worker had a pre-cancerous condition, and the burn triggered a cancer from which he died. The defendant was held liable for his death, not just the burn, because the initial type of injury was foreseeable.