When death is literally the deadline: the “cut-off” point for assessing detriment in proprietary estoppel

Throughout the brief history of proprietary estoppel, it has been rare to find a case where it was argued that the promisor passed away before the promisee suffers sufficient detriment. Rarer still, to find this promise made jointly by co-owners as tenants-in-common of a property. In Cheung Lai Mui v Cheung Wai Shing [2021], the Hong Kong Court of Final Appeal found the “cut-off” point for assessing detriment in such a case to be the death of the last surviving co-owner—but why should it be? This article explores the theoretical interactions between proprietary estoppel, unconscionability and co-ownership in seeking to answer this question.