Category: Claims handling · Reviewed by Tim Roche, Director · PI & Commercial · Last reviewed 2026-06-11
Occurrence-based cover responds to loss, damage, injury or liability arising from an event that occurs during the policy period, regardless of when the claim is later made against the insured.
Occurrence cover is the traditional structure for general liability, employers’ liability, public liability, motor and most property insurance. The trigger is the event itself — the date of the accident, the date of the fire, the date of the injury, the date of the property damage. Whether the underlying third party brings a claim in the same year, three years later, or twenty years later, the policy in force when the event occurred is the one that responds.
The strength of occurrence cover is its predictability for the insured: cover does not depend on continuing to maintain a policy with the same insurer. The weakness is its tail for the insurer: the policy may be called on to respond decades after expiry, by which time the underwriting was based on assumptions long superseded. Long-tail occurrence exposures — mesothelioma, abuse, environmental — have produced some of the most prolonged and expensive coverage disputes in English insurance history.
Occurrence cover is governed by the policy wording, construed under English contract law principles and the Insurance Act 2015. The leading English authorities on the operation of occurrence triggers in long-tail business are:
The Employers’ Liability Tracing Office (ELTO) database — a centralised system holding records of employers’ liability policies — was created to allow long-tail claimants to find the relevant insurer many years after exposure. Insurers operating in the UK EL market must contribute records to ELTO.
For motor business, the Road Traffic Act 1988 and the MIB (Motor Insurers’ Bureau) Untraced Drivers Agreement and Uninsured Drivers Agreement provide a backstop where the insurer cannot be identified or has gone insolvent.
For a simple occurrence claim, trigger analysis is straightforward. The handler establishes the date of the event, identifies the policy in force on that date, and the claim sits with that policy. For most everyday motor, property and PL claims this happens within seconds at FNOL.
For long-tail occurrence claims, complexity emerges. The handler must identify the policies in force across the period of exposure. For a mesothelioma claim arising from asbestos exposure between 1962 and 1981, that may mean tracing eight different EL insurers, allocating exposure between them, and managing contribution between them.
The London Market’s Asbestos Working Party historically agreed protocols for handling mesothelioma claims that allowed insurers to share the cost on a defined formula (years of exposure, dose, employer’s history) rather than litigating allocation each time. Similar protocols exist for environmental claims and abuse compensation.
For property occurrence, the date of the event is usually the date of the immediate physical incident (the fire, the flood, the storm). For business interruption following physical damage, the trigger is the property damage; the BI cover follows. For some property losses with delayed manifestation (gradual subsidence, hidden water ingress), the trigger date is contested — the wording usually has a “first manifest” provision to resolve this.
For long-tail liability, the handler must consider not only which policy responds, but also the apportionment between policies if exposure straddled multiple years. The apportionment is governed by the wording’s allocation provisions (if any), by precedent, and by the parties’ agreement.
“Per-occurrence” limits apply where multiple losses from a single event aggregate to a single limit. The definition of “occurrence” then becomes critical and is the subject of dedicated coverage analysis. Axa Reinsurance v Field [1996] 1 WLR 1026 is the leading English authority on what counts as an occurrence for reinsurance aggregation purposes.
“Continuous trigger” or “spread trigger” theories — that an exposure spread over multiple years triggers each year’s policy concurrently — are more developed in US law than English. English courts have largely rejected spread trigger where the wording does not expressly support it.
“Manifestation” triggers are functionally similar to occurrence in some wordings but operate by reference to when the loss becomes apparent rather than when the event occurred. Modern English property wordings have largely moved away from manifestation language.
“Aggregate” occurrence limits cap the policy’s exposure across all occurrences in the period, in contrast to “per occurrence” limits which cap the exposure to a single occurrence. Both structures are common.
A construction company’s £10m EL policy in force in 1976 is presented with a 2024 mesothelioma claim from a former employee whose exposure to asbestos occurred between 1972 and 1979. The trigger is the year(s) of exposure. Three insurers respond: the 1972-1974 insurer, the 1975-1977 insurer (the one in question, which carries the largest exposure window) and the 1978-1979 insurer. Under the historic London Market protocol the three insurers share on a time-on-risk basis, with the 1975-1977 insurer paying 3/8ths of the £180,000 settlement (£67,500). The Compensation Act 2006 section 3 makes the construction company jointly and severally liable to the claimant; the insurers’ apportionment is between themselves.
By Matt Bartlett, Director, on 2026-06-11. Next review: 2026-12-11.
This entry is part of the Apex Insurance Wiki. Last reviewed by Matt Bartlett on 2026-06-11. Apex Insurance Brokers Limited, FCA FRN 724952, Companies House 07014570. Not regulated advice — consult your broker on your specific position.
Apex Insurance Brokers serves UK professional services firms and commercial businesses. Call 0117 325 0027, email hello@apexinsurancebrokers.co.uk, or request a quotation.
Get a quote