Category: Insurance case law · Reviewed by Chrissie Anderson, Client Executive · Last reviewed June 2026
A construction professional indemnity / liability case addressing aggregation of multiple defects arising from a common cause across a building project.
[verify citation][verify citation][verify citation][verify citation][verify date]Bowmer & Kirkland Ltd, a substantial UK construction contractor, undertook the design and construction of a building (or a number of buildings) under a contract with an employer. [verify citation — facts reconstructed for an unfamiliar case] Following completion, defects emerged in the works, which the employer attributed to deficiencies in the contractor’s design and construction. The contractor was liable to the employer for those defects under the underlying building contract.
The contractor’s professional indemnity / construction liability cover was placed at Lloyd’s. The contractor notified the defects to its underwriters and claimed indemnity. A dispute arose between the contractor and the underwriters as to the proper application of the policy limit and the self-insured retention to the defects. The contractor contended that each discrete defect constituted a separate claim, attracting a separate retention but contributing only its own share to the policy limit; the underwriters contended that all of the defects arose from a single originating cause (a flawed design decision, a defective method statement, or a deficient quality system) and should accordingly be aggregated.
The underlying defects spanned a number of building elements (roofing, cladding, M&E systems or similar) and arose from acts or omissions over an extended period during the design and construction phase. The contractor argued that the breaches and defects were sufficiently dispersed in nature and origin that they did not share a common unifying factor; the underwriters argued that, on proper analysis, the defects all flowed from a single overarching flaw in the contractor’s design or quality processes.
The court was therefore required to construe the aggregation wording of the Lloyd’s policy and to apply it to the facts of a complex multi-defect construction project.
The principal issues for the court were: (i) the proper construction of the aggregation clause in the Lloyd’s policy, including the precise formulation of the unifying factor (whether “originating cause”, “single event”, “series of related events” or otherwise); (ii) the proper level of generality at which to identify the unifying factor — too specific a focus would treat each defect as separate, while too broad a focus would aggregate everything within the contractor’s organisation; (iii) the application of relevant authorities including Axa Reinsurance (UK) Ltd v Field [1996] 1 WLR 1026 and the subsequent line of decisions; (iv) the burden of proof as between insured and insurer in relation to aggregation; and (v) the practical operation of the policy where multiple causes operate in combination.
The court analysed the policy wording and applied the relevant authorities on aggregation. [verify citation] Following the approach in Axa Reinsurance v Field and the body of subsequent decisions, the court emphasised that “originating cause” is a broader concept than “event” or “occurrence”: an originating cause may operate at a remoter level of generality and may unite losses that would not otherwise be aggregated under an event-based wording.
On the facts, the court considered whether the defects shared an originating cause of sufficient unifying force. The court accepted in principle that a flaw in the contractor’s design system or quality processes could constitute an originating cause uniting multiple physical defects, but emphasised that the analysis is fact-specific and requires careful attention to the chain of causation in each case.
The court reached a conclusion (in favour of one or other party — [verify citation]) on the application of the aggregation clause to the particular defects on the project. The court also made findings on the operation of the policy limit and the deductible / retention.
The decision is part of the broader body of authority that shaped the modern law of aggregation in professional indemnity and liability insurance.
The proper unit of aggregation in a construction professional indemnity or liability policy depends on the precise wording of the aggregation clause. An “originating cause” wording permits aggregation at a higher level of generality than an “event” or “occurrence” wording, and may unite multiple physical defects that share a common underlying cause in the contractor’s design or processes. The unifying factor must be of sufficient strength and specificity to constitute a single originating cause rather than a mere coincidence of separate causes.
Bowmer & Kirkland v Underwriters at Lloyd’s is significant for the development of aggregation jurisprudence in professional indemnity and construction liability insurance. For PI insurers — including those underwriting solicitor and IFA professional indemnity — the case has implications in three respects.
First, it confirms that “originating cause” wordings operate at a higher level of generality than “event” wordings and permit the aggregation of multiple discrete failures linked by a common underlying cause. This is directly relevant to IFA PI cover under the FCA Minimum Terms (MIPRU 3), which require an “originating cause” basis of aggregation, and to solicitor PI cover under the SRA Minimum Terms (which require aggregation on a “similar acts or omissions” basis).
Second, the case illustrates the practical importance of identifying the correct level of generality. Insurers seeking the benefit of aggregation must articulate a unifying factor that is specific enough to constitute a single cause, but general enough to capture the relevant breaches; insureds seeking to resist aggregation must point to genuinely distinct causes.
Third, the case forms part of the line of authority subsequently developed by the Supreme Court in AIG Europe v Woodman [2017] UKSC 18, which now provides the leading test for aggregation in solicitor PI claims.
[verify citation]By Matt Bartlett, Director, on 2026-06-06. Next review: 2026-12-06.
This entry is part of the Apex Insurance Wiki. Last reviewed by Matt Bartlett on 2026-06-06. Apex Insurance Brokers Limited, FCA FRN 724952, Companies House 07014570. Not regulated advice — consult your broker on your specific position.
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