7.2 Concurrent and Successive Causes

Concurrent Causes — The Two Causes Rule

A loss frequently has two or more causes operating at the same time, each of which is sufficiently dominant to be a proximate cause. This is the situation of concurrent causes. English law, developed in the common law and applied alongside section 55 of the Marine Insurance Act 1906, resolves these cases by looking at the legal character of each rival cause: is the second cause uninsured (but not excepted), or is it excepted (excluded) by the policy? The answer determines whether the insured can recover.

This is sometimes called the two causes rule in IF1 materials.

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Rule 1 — Insured Peril + Uninsured (Non-Excepted) Peril: Insurer IS Liable

Where two concurrent causes operate together to produce the loss, one an insured peril and the other an uninsured peril that is not excluded by the policy, the insurer is generally liable. The insured peril is still a proximate cause, and the uninsured peril is legally irrelevant because the parties did not agree to exclude it.

The leading authority is JJ Lloyd Instruments Ltd v Northern Star Insurance Co Ltd (The Miss Jay Jay) [1987] 1 Lloyd's Rep 32. A yacht was lost through a combination of perils of the sea (insured) and negligence of the crew (uninsured but not excluded). The Court of Appeal held that where one proximate cause is insured and the other is uninsured but not excepted, the insurer is liable.

Example: A property policy covers storm but is silent on sprinkler leakage. A storm damages the sprinkler system, which then leaks and ruins stock. Storm and sprinkler leakage operate together. Sprinkler leakage is uninsured but not excluded, so the insurer is liable for the storm-damage and the consequent stock loss — the insured peril (storm) is a proximate cause, and the mere uninsured peril does not defeat it.

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Rule 2 — Insured Peril + Excepted (Excluded) Peril: Insurer is NOT Liable

Where the concurrent causes are an insured peril and an excepted peril (a peril the policy expressly excludes), the insurer is not liable. The exclusion prevails over the insured peril.

The leading authority is Wayne Tank and Pump Co Ltd v Employers' Liability Assurance Corp Ltd [1974] QB 57. Two causes of equal efficiency operated together: negligence of the insured (insured under a public liability policy) and an inherent vice in the insured's own product (excluded). The Court of Appeal held that where an insured peril and an excepted peril operate concurrently, the exclusion prevails and the insurer is not liable.

The rule was reaffirmed by the Court of Appeal in University of Exeter v Allianz [2023] EWCA Civ 1484. A Second World War bomb was dropped in 1942 and detonated in a controlled explosion in 2021; both the original dropping and the modern detonation were treated as concurrent causes, and the war exclusion prevailed, defeating the claim.

Example: A property policy insures against storm but excepts flood. A severe weather event produces both storm-driven rain and river flooding at the same time, and both together destroy the building. Storm is insured, flood is excepted, and they operate concurrently. Under the Wayne Tank rule, the exclusion for flood prevails and the insurer is not liable for the loss.

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The Two Causes Rule — Comparison Table

The whole table can be compressed into a single exam sentence: an insured peril beats an uninsured peril, but an excepted peril beats an insured peril.

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Successive Causes and the Intervening Cause

A loss may also have a successive chain of causes, with one event following another over time. If the chain is unbroken and the original insured peril remains the dominant efficient cause throughout, the original insured peril is the proximate cause (as with the fire-collapse scenario in section 7.1). But if a new, independent cause intervenes and becomes the dominant cause of the loss, the chain is broken and the intervening cause becomes the proximate cause.

An intervening cause (sometimes called a novus actus interveniens) is therefore a fresh event that displaces the earlier cause. Whether an intervening event breaks the chain is a question of fact and common sense — the same dominant-efficient-cause test applied across time.

Example — chain not broken: A fire (insured) damages a wall. The wall is left in a precarious state and collapses a week later in ordinary weather. The collapse is the natural consequence of the fire damage; the chain is not broken, and fire remains the proximate cause.

Example — chain broken: A fire (insured) damages a roof. Before the owner can repair it, an unrelated storm (an uninsured peril under this policy) tears the weakened roof away. If the storm is the dominant cause of the final loss, the storm is the new proximate cause; if storm is uninsured, the claim for the later damage fails. If, however, the fire damage was itself the dominant cause and the storm merely accelerated an inevitable collapse, fire remains the proximate cause and the claim succeeds. The answer turns on which cause was, in fact, dominant and efficient.

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No Identifiable Dominant Cause — The Popi M

Where the evidence does not allow the court to identify any single dominant cause, the claim fails. The burden of proof is on the insured, and a court must not invent a cause to fill the gap. This is the rule of Rhesa Shipping Co SA v Edmunds (The Popi M) [1985] 1 WLR 948: where two possible causes are both consistent with the evidence but neither is proved to be the dominant one, the insured has not discharged the burden and the insurer is not liable.

This applies with equal force to concurrent-cause cases: the insured must prove that an insured peril was, on the balance of probabilities, a proximate cause. Speculation is not enough.

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The Loss-of-Life Proviso

Some life and personal accident policies, and certain marine wordings, contain a loss-of-life proviso. The proviso provides that, where loss of life or personal injury is caused by an insured peril, the insurer remains liable even if an excepted peril contributed to the loss. In effect, for death or injury claims the usual Wayne Tank rule (excepted peril overrides insured peril) is modified by the wording: the insured peril still attracts cover.

This is a feature of policy drafting rather than a universal rule of statute, and IF1 candidates should treat it as a wording-driven exception. The nearest statutory analogue is section 55(2)(a) of the Marine Insurance Act 1906, which provides that even where the wilful misconduct of the assured would otherwise exclude cover, the insurer remains liable for any loss proximately caused by an insured peril even though the loss would not have happened but for the negligence of the master or crew. The same principle — an insured peril prevailing over an excepted peril in defined circumstances — underpins the loss-of-life proviso found in many wordings.

Example: A personal accident policy covers accidental death but excepts war. The insured is killed in a terrorist act during a war. Without a loss-of-life proviso, the war exception would defeat the claim under the Wayne Tank rule. With a loss-of-life proviso, the insured peril (violent accidental injury) prevails and the policy pays, because the proviso is drafted to modify the exclusion for death claims.

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Worked Scenario — Concurrent Causes in Practice

A factory is insured under a property policy that covers fire and storm and excepts flood and terrorism. During a single severe weather event, the following occur together:

• High winds (storm — insured) tear off part of the roof.
• River water (flood — excepted) inundates the ground floor.
• A resulting electrical fault causes a fire (insured).

The fire and storm damage is payable to the extent it can be separately identified, because insured perils are proximate causes of those parts of the loss. The flood damage is not payable, because flood is an excepted peril operating concurrently and the Wayne Tank rule bars recovery for that part. Where insured and excepted perils cause indivisible damage together, the excepted peril prevails for the indivisible loss. This fact-sensitive apportionment is typical of concurrent-cause claims handling.

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Common Exam Pitfalls

• Do not treat an uninsured peril the same as an excepted peril. Uninsured-but-not-excluded leaves cover intact (The Miss Jay Jay); excepted overrides cover (Wayne Tank).
• Do not assume the most recent event is the proximate cause in a successive chain. Ask which cause is dominant and efficient.
• Do not assume an intervening event always breaks the chain. It only does so if it is new, independent, and dominant.
• Remember the burden of proof: if the insured cannot prove an insured peril was a proximate cause, the claim fails (The Popi M).
• Remember that a loss-of-life proviso is wording-driven; do not assume it applies to every policy or to non-death claims.

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Key Takeaways

• Where an insured peril and an uninsured (non-excepted) peril operate concurrently, the insurer is liable — the uninsured peril is legally irrelevant (The Miss Jay Jay).
• Where an insured peril and an excepted peril operate concurrently, the insurer is not liable — the exclusion prevails (Wayne Tank; University of Exeter v Allianz).
• In a successive chain, a new, independent, dominant intervening cause breaks the chain and becomes the new proximate cause.
• Where no dominant cause can be proved, the claim fails — the burden of proof is on the insured (The Popi M).
• A loss-of-life proviso in certain wordings modifies the excepted-peril rule so that, where death is caused by an insured peril, the insurer remains liable even if an excepted peril contributed; section 55(2)(a) MIA 1906 reflects a similar principle for master/crew negligence.