Novus actus interveniens — a new intervening act — is the common-law doctrine that a fresh, independent event occurring after the defendant's breach can sever the chain of causation between that breach and the claimant's loss. Where it applies, the original wrongdoer is treated in law as not having caused the further loss that flows from the intervening event, even though, but for the original breach, that event might never have arisen.
In professional indemnity claims against solicitors, accountants, surveyors and other regulated professionals, novus actus is one of the sharpest tools an insurer's defence team has for reducing exposure. It sits alongside the but-for test and the doctrine of remoteness of damage, and the three are often argued together.
There is no single formulation, but the appellate authorities converge on three overlapping questions:
In Knightley v Johns [1982] 1 WLR 349 the Court of Appeal held that a police inspector's negligent decision to send a motorcyclist the wrong way through a tunnel broke the chain from the original driver whose crash had caused the road closure — the later act was new, intervening and so unreasonable that it eclipsed the earlier negligence. By contrast, in Corr v IBC Vehicles [2008] UKHL 13 the House of Lords held that a claimant's suicide, following depression caused by a workplace accident, did not break the chain: the suicide was a foreseeable consequence of the injury negligently caused. Reeves v Commissioner of Police [2000] 1 AC 360 reached a similar result on different facts — the suicide of a prisoner in police custody was foreseeable and the very risk the duty was there to guard against. In Lamb v Camden LBC [1981] QB 625 squatters occupying a house made uninhabitable by the council's negligence were held to be a novus actus; their conduct was extraneous and could not fairly be laid at the council's door.
The most common novus actus argument in PI claims involves a second professional instructed to remedy the first professional's error. Insurers for the first professional often argue that the second professional's own negligence breaks the chain. English courts are generally unsympathetic to that argument. Where the first breach makes the second professional's involvement foreseeable, the second professional's negligent handling is typically treated as a foreseeable secondary consequence rather than a true intervening act. The first professional remains liable for the loss the client would have avoided but for the original breach, with the second professional joined as a contributor.
Worked example. Solicitor A misses a limitation deadline on a personal injury claim worth an assessed £180,000. The client instructs Solicitor B to bring a professional negligence claim against A. B negligently miscalculates the value of the lost underlying claim and settles A's PI liability at £90,000. The client sues both. Does B's negligence break the chain from A? On orthodox principles, usually not. A's original breach gave rise to B's involvement; B's error is a foreseeable secondary consequence; and it is not so unreasonable or extraneous as to eclipse A's original wrong. A's PI insurer is likely to remain liable for the residual loss, with a contribution claim against B under the Civil Liability (Contribution) Act 1978. Illustrative only — outcomes turn on the specific facts and evidence.
A claimant who acts unreasonably after the breach — refusing sensible mitigation, declining a reasonable settlement offer, or embarking on a course no prudent person in their position would take — may find that the additional loss falls the other side of a novus actus line. The mitigation duty and the novus actus doctrine overlap here. A claimant does not lose the whole claim; they lose the incremental loss the unreasonable act generated.
Market movements, regulatory changes and third-party insolvencies sometimes intervene between breach and loss. Whether they break the chain depends on foreseeability and proximity. A collapse in property prices between a negligent valuation and enforcement may reduce recoverable loss under SAAMCO scope-of-duty principles, but it will not usually amount to a novus actus in the strict sense.
Defendant insurers use novus actus in three main ways: to shift the whole loss onto a later actor; to reduce the recoverable quantum to the loss caused up to the intervening event; and to strengthen a contribution claim under the 1978 Act. A well-pleaded response requires precise chronology, evidenced foreseeability, and careful cross-reference to the solicitors' PI insurance, accountants' PI insurance or surveyors' PI insurance policy wording under which cover is sought.
Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Firm reference number 724952. This entry is general information, not advice on any particular policy.