The Commercial Court has decided that the 9/11 terrorist attacks on the World Trade Center constituted two events and not one, the first time an English court has ruled on this issue.

In Aioi Nissay Dowa Insurance Company v Heraldglen Limited and Advent Capital (No. 3) Limited [2013] EWHC 154 (Comm), Mr Justice Field upheld the decision of an arbitral panel which concluded that for the purposes of four retrocession excess of loss reinsurance agreements, there was not sufficient unity in time or location for the losses to have arisen out of a single event.

In deciding the case, Field J analysed the "unities" doctrine, which developed from the Dawson's Field Arbitration in 1972 and was clarified by Mr Justice Rix in Kuwait Airways Corporation v Kuwait Insurance Co SAK [1996] 1 Lloyd's Rep 664. As Rix J said in Kuwait Airways, although one occurrence may embrace several losses, the circumstances of the losses must be scrutinised to see whether they involve such a degree of unity as to justify their being described as or arising out of one occurrence. In assessing the degree of unity under the doctrine, regard may be had to such factors as cause, locality, time, and the intentions of the human agents. Ultimately, the doctrine is an exercise of judgment.

When considering the WTC losses, Field J held that the arbitral tribunal had not erred in considering the four unifying factors. In particular, although the hijackings were part of a single terrorist plot, this did not amount to an event of sufficient causative relevance to override the conclusion that there were two separate hijackings of two separate aircraft which caused separate loss and damage.

Field J recognised that the two event conclusion was different from that reached by the US Court of Appeals, Second Circuit, in World Trade Center Properties v Hartford Fire Insurance Co [2003] 345 F.154, where it was held that the WTC loss resulted from a single occurrence for aggregation purposes. However that case depended on different, broader aggregation wording where "occurrence" was defined as encompassing losses attributable directly or indirectly to one cause or one series of similar causes. Further, that US decision on the so-called 'Wilprop' wording did not apply to insurers on different policy forms, where the definition of "occurrence" was vaguer and the attacks were deemed multiple occurrences.