The case of Castellain v Preston [1883] laid down an important principle regarding what feature of insurable interest?

The principle established in the case of Castellain v Preston [1883] primarily focuses on the subject-matter of insurance, clarifying that a valid insurable interest must relate to something in which the insured has a legitimate stake or connection. The ruling emphasized that the existence of an insurable interest is critical for the enforceability of an insurance contract, which hinges on the connection between the individual and the subject of the policy. In this context, the subject-matter of the contract refers to the specific items or interests being insured—essentially the property, liability, or risk involved in the insurance agreement.

While other aspects, such as the existence of a legal relationship and the financial value of the subject-matter, are important in determining the nature of the insurable interest, they do not encapsulate the fundamental aspect focused on in this case. The core principle revolves around ensuring that the entity purchasing the insurance has a direct and tangible interest in the subject-matter, which protects against moral hazard and reinforces the integrity of the insurance contract.