In the Supreme Court, SIB argued its loss was the loss of the chance to discharge the debts of the early customers for a few pence in the pound; that is, the difference between the payment to the early customers of 100 pence in the pound, and the dividend those early customers would have received if they had to prove in the liquidation.
Lady Rose, writing for the majority, rejected this argument. If HSBC had complied with its Quincecare duty and disobeyed Mr Stanford's instruction to pay out SIB's money, the counterfactual was that SIB would have an extra £116m to its credit, and would not have discharged any of the payments due to the early customers. The class of creditors entitled to prove in the liquidation would therefore be swelled, and there would be no distinction between "early" and "late" customers. Lady Rose held that the "chance" of being able to discharge a debt owed to an early customer by paying them, for example, 12 pence instead of the 100 they were in fact paid, was matched by the "risk" of having to pay the late customers 12 pence instead of five. The chance therefore must be quantified as the same as the risk.
Lord Leggatt, writing separately, concurred with the outcome, and similarly found that SIB's argument was flawed because it disregarded the net loss rule: the basic rule that in awarding damages for breach of contract or in tort, losses and gains arising from the breach must be netted off against each other. Lord Leggatt considered also whether the recent BTI v Sequana case, in which the Supreme Court affirmed that directors of an insolvent company owe a fiduciary duty to have regard to the interests of its creditors, could impact the analysis. He held it could not, because it "would be contrary to first principles to posit that, at some (imprecise) point on a path that leads to a company going into insolvent liquidation, the nature of its legal personality changes, such that, from then on, any disposition of the company’s assets is treated as a loss to the company even if it discharges a liability and so leaves the company’s net asset position unchanged". He emphasised the need for clear rules and legal certainty in the insolvency context.