Legal Case Summary
Chester v Afshar [2004] 3 WLR 927
Establishing causation following consent to medical treatment and subsequent injury.
Facts
The claimant Chester, had managed with bad back pain for several years, which severely limited her ability to walk around and interfered with her ability to control her bladder. A medical examination and test revealed a problem with her spinal cord, and subsequently her doctor, the defendant, advised that she undergo surgery to remedy the problem. Notably, this surgery carried a very minor risk (1% approximately) that it would in fact worsen the issue, however the claimant had not been warned of this risk by the defendant. The claimant agreed to the operation, which was carried out responsibly, however she fell within the 1%. The claimant subsequently submitted she may not have consented to the surgery had she been aware of the possible risks. At first instance, the judge determined that whilst the defendant had not been negligent in his surgical performance, he was liable for having failed to adequately inform the claimant of the risks, as had the operation been performed on an alternative date, her injuries may not have been exacerbated. At first appeal, the Court of Appeal approved the initial judgment.
Issues
The defendant appealed, submitted that there was no causation as the likelihood of the claimant having consented to the operation at some point did not alter the fact that the operation bore risks.
Decision / Outcome
The House of Lords dismissed the appeal (in a 3 – 2 split decision), holding that the defendant had failed in his tortious professional duty, satisfying the ‘but for’ test, and that the claimant deserved a remedy.
Updated 19 March 2026
This summary remains broadly accurate as a description of Chester v Afshar [2004] UKHL 41. The House of Lords decision is correctly described: the majority (3–2) held the defendant liable in negligence for failing to warn the claimant of the risk of cauda equina syndrome, and found causation established notwithstanding the orthodox difficulties with the ‘but for’ test in these circumstances. The case citation given ([2004] 3 WLR 927) is accurate, though the neutral citation [2004] UKHL 41 is the authoritative reference.
One point of legal context worth noting for readers: the decision in Chester v Afshar has since been considered alongside the Supreme Court’s important later ruling in Montgomery v Lanarkshire Health Board [2015] UKSC 11. Montgomery substantially reformulated the law on informed consent in medical negligence, moving away from the Bolam-based approach and establishing that patients must be told of material risks. Chester remains good law on causation in this specific context, but its practical significance now falls squarely within the framework set by Montgomery, which students should read alongside it. No legislation has displaced these principles, and no subsequent Supreme Court decision has overruled Chester.
