Informed Consent to Medical Treatment Post-Montgomery: Causation and Coincidence.

If a patient suffers physical harm during medical treatment when a risk materialises which the doctor failed to warn the patient about, there are two key issues when a negligence claim is brought by the patient. First, it must be shown that the doctor was negligent in failing to warn the patient about the particular risk. Secondly, it must normally be shown that this failure to warn was a cause of the damage suffered, although courts also allow claims to succeed when a patient may still have undergone treatment even if adequately warned. The recent decision in Montgomery v Lanarkshire HA [2015] UKSC 11 changes the test for the first of these steps, by moving away from asking what a reasonable doctor would warn about and asking instead what a reasonable patient, or indeed the actual patient, would want to know. This article considers how that change ought to impact on the second step, causation. The first part of this article traces the development of the law on the standard of disclosure of risks, from Sidaway to Montgomery in order to expose the place that patient autonomy now occupies and the conception of autonomy that underlies the decisions. The second section addresses the causation issues arising in cases of medical non-disclosure of risk, and includes but is not limited to discussion of Chester. It first considers the modified objective approach to proof of causation adopted in Canada and argues that English law would be wise to reject such a development. The Chester problem is then addressed, and the analysis will focus primarily on what is actually meant by 'coincidence' since this term is often used but rarely explained. Finally, considering the situation that arises when the risk that materialises is different from the risk about which the doctor failed to warn the patient, it argues for a closer delineation of the relevant risks in English law.