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Causation

Lecture L6 Negligence — Element 3 Reading: Horsey & Rackley ch 9; Nolan & Oliphant ch 6

Snapshot

Causation is two questions a claimant must answer affirmatively before damages flow. The factual question (cause-in-fact) asks whether D's breach made a difference — orthodoxy is the but-for test, with three relaxations: material contribution to harm (Bonnington), material contribution to risk (the Fairchild exception), and a narrow loss of a chance doctrine. The legal question (cause-in-law) asks whether the chain has been broken by an intervening act (novus actus interveniens) and whether the damage is too remote — remoteness proper is Topic 7. This page covers the rest.

1. The but-for test

The starting (and usually finishing) point is the counterfactual but-for test: would C's harm have occurred but for D's breach? If the answer is "yes, it would have happened anyway", causation fails and the claim ends. C bears the onus on the balance of probabilities: anything above 50% is treated as established to 100%.

Barnett v Chelsea & Kensington HMC [1969] 1 QB 428

Facts: A nightwatchman attended A&E with vomiting; the on-duty doctor negligently refused to examine him. He was sent home and died hours later of arsenic poisoning.
Holding: The hospital breached its duty, but the claim failed on causation: medical evidence showed the antidote could not have been administered in time, so death would have occurred even with proper care.
Why it matters: Textbook illustration of breach without causation — a finding of breach is necessary but not sufficient.

Compare McWilliams v Sir William Arrol & Co Ltd [1962] 1 WLR 295: employer failed to provide a safety belt, but the deceased habitually refused to wear one — breach made no difference. Where C is exposed to several distinct possible causes (only one tortious), C must still pin harm on D's breach on the balance of probabilities.

Wilsher v Essex AHA [1988] AC 1074 (HL)

Facts: A premature baby suffered retrolental fibroplasia (blindness) following negligent over-administration of oxygen; four innocent neonatal conditions were also possible causes, and science could not say which had triggered the injury.
Holding: Claim failed: where C is exposed to multiple distinct causal agents and cannot show on the balance of probabilities that the tortious agent caused the harm, causation is not established. McGhee distinguished as a single-agent case.
Why it matters: Marks the outer limit of any relaxation of but-for: with different-kind agents, C must still pin harm on D's breach.

2. Material contribution to harm

The first relaxation arises where harm is the cumulative product of several causes acting concurrently through the same mechanism — typically an industrial disease from a single agent received from multiple sources. Strict but-for would defeat such claims since no single source is sufficient. C succeeds on proof that D's breach made a material contribution (more than de minimis) to the injury.

Bonnington Castings Ltd v Wardlaw [1956] AC 613 (HL)

Facts: The pursuer contracted pneumoconiosis from silica dust at work — some from a pneumatic hammer (innocent) and some from grinders with defective extraction (tortious). It was impossible to say which particles caused the disease.
Holding: Causation established: sufficient that the tortious dust made a material (more than negligible) contribution to the disease.
Why it matters: Anchor authority for cumulative-cause cases: the breach need not be the sole or dominant cause, only a non-trivial contributor.

The doctrine has migrated into clinical negligence where breach and innocent cause act through a single pathological process.

Bailey v Ministry of Defence [2008] EWCA Civ 883

Facts: C weakened by combination of negligent post-op care and unrelated pancreatitis; aspirated vomit, suffered brain damage. Science could not divide the two contributions.
Holding: Where breach and non-tortious cause acted cumulatively to produce indivisible injury and but-for failed through scientific gap, C succeeded on material contribution.
Why it matters: Confirms Bonnington applies in medical contexts and where contributing causes are not all tortious.

Williams v Bermuda Hospitals Board [2016] UKPC 4

Facts: 2h 20m negligent delay treating appendicitis allowed sepsis to progress, causing myocardial damage from a single continuing process.
Holding: Material contribution applies even where causes are successive, provided they operate through one continuing process.
Why it matters: Extends Bonnington beyond simultaneous-exposure; standard tool for clinical-negligence indivisible injuries.

Four conditions structure a Bonnington argument: (i) single agent/process (not Wilsher's multiple distinct agents); (ii) breach; (iii) more than de minimis contribution; (iv) indivisible injury — if divisible, D pays only the apportioned share (Section 5).

3. Material increase in risk & the Fairchild exception

A narrower relaxation operates where even material contribution to harm cannot be proved because science cannot say whether breach caused or merely raised the risk. In tightly limited circumstances C succeeds on proof D materially increased the risk.

McGhee v National Coal Board [1973] 1 WLR 1 (HL)

Facts: Pursuer contracted dermatitis from brick-kiln dust; employer's only breach was failing to provide showers, prolonging skin exposure during cycle home. Science could not say whether disease arose at work or after.
Holding: Sufficient that breach materially increased the risk of disease.
Why it matters: First authority equating material increase in risk with material contribution to harm; later confined to single-agent cases.

Fairchild v Glenhaven Funeral Services [2002] UKHL 22

Facts: Mesothelioma victims negligently exposed to asbestos by successive employers; science could not identify which fibre triggered disease (a single fibre may suffice, and any tortious exposure could be the operative one).
Holding: Special rule: where (a) mesothelioma, (b) single agent (asbestos), (c) multiple negligent defendants, (d) gap is one of medical knowledge — each defendant who materially increased risk is liable in full, joint and several.
Why it matters: Leading modern authority on causation exceptions; carefully limited to single-agent cases, distinguishing Wilsher where multiple different agents made causation impossible.

Barker v Corus UK Ltd [2006] UKHL 20

Facts: Mesothelioma victim exposed by two employers and innocently when self-employed.
Holding: Fairchild liability is for the increase in risk, so apportioned severally by each D's share of exposure; joint-and-several rejected.
Why it matters: Reframed Fairchild liability as risk-based; Parliament intervened almost immediately for mesothelioma.

Compensation Act 2006, s.3

For mesothelioma cases within the Fairchild exception, the Act restores joint-and-several liability: any responsible negligent employer is liable for the whole damage and may seek contribution. Section 3 reverses Barker for mesothelioma only; the Barker principle survives at common law for any other Fairchild-style claim (see Zurich Insurance v IEG [2015] UKSC 33).

Sienkiewicz v Greif (UK) Ltd [2011] UKSC 10

Facts: C negligently exposed to low-level asbestos by a single employer alongside background environmental exposure; died of mesothelioma.
Holding: Fairchild applies against a sole defendant on a more-than-de-minimis increment; mesothelioma is "in a category all their own".
Why it matters: Confirms Fairchild operates against single tortfeasors; signals reluctance to extend beyond mesothelioma.

Heneghan v Manchester Dry Docks Ltd [2016] EWCA Civ 86

Facts: Deceased exposed to asbestos by six employers (35.2% of total dose); died of asbestos-induced lung cancer.
Holding: Fairchild extended to lung cancer (shares mesothelioma's unusual features); damages apportioned under Barker as the 2006 Act doesn't cover lung cancer.
Why it matters: Cleanest example of Fairchild beyond mesothelioma; illustrates pro-rata apportionment regime.

Five elements of McGhee/Fairchild: (i) single agent could have caused harm; (ii) C exposed both tortiously and innocently; (iii) breach preceded harm; (iv) C can only show breach materially increased the risk; (v) disease has mesothelioma's "unusual features" (long latency, single-fibre sufficiency, source attribution impossible).

4. Loss of a chance

Can C reframe a failed but-for case as diminution of the chance of a better outcome? English courts say no for personal injury and clinical negligence (commercial loss-of-chance differs, e.g. Allied Maples v Simmons & Simmons).

Hotson v East Berkshire AHA [1987] AC 750 (HL)

Facts: 13-year-old fell from a tree; hospital negligently failed to diagnose hip fracture for five days. Even prompt diagnosis gave only 25% chance of avoiding necrosis.
Holding: On the balance of probabilities the injury was caused by the fall, not the delay; no recoverable "lost 25% chance".
Why it matters: Rejects loss-of-chance for past-fact issues; the 50%+ threshold is a hard cliff.

Gregg v Scott [2005] UKHL 2

Facts: GP misdiagnosed malignant lump as benign; nine-month delay reduced 10-year survival chance from 42% to 25%. C alive at trial.
Holding: 3-2 majority rejected loss-of-chance; Lord Hoffmann cited policy (insurer/NHS liability, erosion of balance-of-probabilities standard).
Why it matters: Definitive modern rejection of loss of chance in clinical negligence; "all-or-nothing" prevails.

5. Multiple sufficient causes — divisible v indivisible injury

Where the same agent cumulatively produces a disease whose severity is dose-dependent (divisible: asbestosis, pneumoconiosis, noise-induced hearing loss), each D pays only its share. An indivisible injury (death, mesothelioma, brain damage) cannot be carved up; each contributor is liable for the whole, subject to contribution.

Holtby v Brigham & Cowan (Hull) Ltd [2000] 3 All ER 421 (CA)

Facts: C developed asbestosis after exposure by several employers; half attributable to D.
Holding: Asbestosis is divisible (severity scales with dose); D liable only for its apportioned share.
Why it matters: Establishes apportionment for divisible injuries; contrasts with mesothelioma under Fairchild/2006 Act.

Consequence: in Bonnington/Bailey-type indivisible cases a material contributor pays the whole; in Holtby-type divisible cases each D pays its slice. See also Holmes v Poeton Holdings Ltd [2023] EWCA Civ 1377.

6. Intervening acts (novus actus interveniens)

Legal causation can be defeated by an intervening event so substantial it becomes the operative cause. Three categories.

(a) Third-party acts. A deliberate or grossly negligent act generally breaks the chain; foreseeability of bare possibility is not enough.

Lamb v Camden LBC [1981] QB 625 (CA)

Facts: D negligently fractured a water main, undermining C's empty house; squatters moved in and caused further damage.
Holding: Squatters' acts were a novus actus; for third-party acts the threshold is "very likely", not merely foreseeable.
Why it matters: Stringent threshold for third-party intervention. Compare Stansbie v Troman [1948] 2 KB 48 (duty was to guard against the act, chain held).

(b) C's own act. Unreasonable conduct breaks the chain; reasonable conduct does not.

McKew v Holland & Hannen & Cubitts (Scotland) Ltd [1969] 3 All ER 1621 (HL)

Facts: D's negligence weakened C's leg; C attempted a steep staircase unaided, leg gave way, he jumped and broke his ankle.
Holding: Unreasonable; novus actus broke the chain to the second injury.
Why it matters: Leading authority on C's own act as novus actus; test is unreasonableness, not foreseeability.

Wieland v Cyril Lord Carpets Ltd [1969] 3 All ER 1006

Facts: Neck injury required surgical collar that disrupted C's bifocal use; she fell down stairs.
Holding: Foreseeable consequence; reasonable response; chain not broken.
Why it matters: Foil to McKew: reasonable response to disability is not novus actus.

(c) Natural events. Break the chain only where independent of the breach and would have caused the loss anyway. Carslogie Steamship v Royal Norwegian Government [1952] AC 292: storm en route to repair caused damage the collision would not have — chain broken. Successive-tortfeasor / supervening-illness issues (Baker v Willoughby; Jobling v Associated Dairies) sit on the causation/quantum boundary and are addressed in the remoteness materials.

7. Application framework

Identify breach and damage precisely. Causation links the failure to the harm complained of.
Apply but-for first. Would harm have occurred but for breach, on balance of probabilities? If yes, move to legal causation; if no, ask whether a relaxation applies.
If but-for fails, consider relaxations in order. (a) Single-agent cumulative indivisible harm: Bonnington. (b) Single-agent risk-only cases: McGhee/Fairchild, only if disease has mesothelioma-like features. (c) Multiple distinct agents: Wilsher bars relaxation.
Address divisibility. Indivisible → D liable in full (subject to contribution); divisible → apportionment by exposure (Holtby); mesothelioma → joint-and-several restored by Compensation Act 2006 s.3.
Test for novus actus. Apply Lamb (third party), McKew/Wieland (C's act), natural-event test.

8. Common pitfalls

Reaching for Fairchild when Bonnington applies. Fairchild is for cases where science cannot even show breach contributed to harm — only that it raised risk. Where breach and innocent factor cumulatively cause indivisible injury through a single process (Bailey/Williams), the authority is Bonnington. Treat Fairchild as quarantined to mesothelioma-shaped diseases.

Confusing divisible and indivisible injury. Mesothelioma is indivisible (single fibre may suffice); asbestosis and pneumoconiosis are divisible (severity tracks dose). Same D, same fibres, very different liability rules.

Pleading loss of chance in clinical-negligence problems. After Hotson/Gregg v Scott, English law refuses diminished prospects as a free-standing head of damage in personal injury.

Treating foreseeability as the novus actus test. Lamb: third-party act must be "very likely", not merely foreseeable. McKew/Wieland: C's act tested for reasonableness, not foreseeability.

9. Exam checklist

Identified breach and head of damage precisely; stated which causal link is contested.
Applied but-for (Barnett) explicitly on balance of probabilities.
If but-for fails, considered Bonnington material contribution; checked single-agent/indivisibility prerequisites (Bailey; Williams).
If contribution to harm unprovable, considered Fairchild; checked mesothelioma-like features (Sienkiewicz; Heneghan); flagged Wilsher for multiple agents.
Addressed apportionment — Barker at common law; Compensation Act 2006 s.3 for mesothelioma; Holtby for divisible diseases.
Rejected loss-of-chance in personal injury (Hotson; Gregg v Scott).
Tested for novus actus: Lamb, McKew/Wieland, natural event.
Signposted remoteness as next stage (Topic 7).