Chester v Afshar [2004] UKHL 41; an important English tort law case concerning causation in the context of negligence and informed consent of patients.

Facts Edit

Mrs C was very nervous about her surgery, later medical evidence suggests the possibility of spinal damage (which she eventually sustained) was about 1-2%. The chances of such type of damage is completely random, which the competence of the surgeon has no bearing.

Mrs C's physician omitted to inform her of the possibilities of spinal damage. It was therefore suggested that had she been informed she would have had the surgery at another time, which would probably not have led to the unfortunate result. The claimant therefore argued that the "but for" test was established by the chances of the injury occuring had she been informed.

The dissenters alleged that the surgeon was not negligent, a surgery performed at another time would have had the same risks anyway. The case also involved a very tight "waiting time" of 3 days between consultation and surgery.


3-2 law lords found that there was negligence and that it ought to have been disclosed, because Mrs C was a very nervous patient and would not have undergone the surgery had she been informed of such risk, thus the injury was attributable and within the scope of to the duty to inform.

Sir Denis HenryEdit

C had expressed her concerns to the doctor and had been wrongly reassured, likewise the doctor of the mountaineer (an allusion to the case of SAAMCO and Lord Hoffmann's mountaineering example) also wrongly assured him that his knee would not give way during his expedition, when in fact it doesn't but he suffers injuries anyway. The doctor is not to be blamed for his knee giving way, but for the fact that the mountaineer was on the expedition in the first place. However this changes if his love for mountaineering will not prevent him from going on an expedition with a stuffed knee (or at least it was more likely for him to go on an expedition than not). His knee will give way sooner or later, the doctor has caused him to suffer this injury sooner rather than later.

However Jenny Steele points out that if the claimant had undergone the operation later then the probabilities suggest that the chances of harm would not occur again, thus the whole harm is in issued not just an acceleration of a future harm.

Lord BinghamEdit

Dissented arguing that C failed to prove causation, she merely showed that she would not have consented to the surgery on the 21st of november 1994, not that she would not undergo the surgery at all. And the probability of the injury was the same fand whoever and whenever the operation was done.

Lord SteynEdit

found that the doctor was liable for damages:

  • A surgeon owes a legal duty to the patient to warn him of possible risks involved in the procedure.
  • Right to receive appropriate warning from the doctor is of paramount importance.
  • Identify the legal interest at stake, namely avoidance of occurrence of particular physical injury which the patient is not prepared to accept, and due respect is given to the autonomy and dignity of each patient.
  • But for the negligent failure to warn and on the balance of probabilities the patient would not have suffered such injuries the next time it was performed.

His lordship set aside the causal principle relating to the increase in risk, and found in favour of the claimant. However in contrast to Honoré, Lord Steyn's reasoning was based more on the importance of patient autonomy in order to:

  • Avoid occurrence of injury not prepared to accept. Easily recognisable as a duty of care.
  • Due respect and dignity for each and every patient. Justifies suspension of causal principles

Lord HoffmannEdit

Lord Hoffmann also dissented alongside Lord Bingham, the failure to warn did not cause the damage, the damage would have happened regardless of warning. His lordship discredits the argument that had C been told and delayed her operation on the balance of probabilities the next time it was conducted she would not have been injured.

The paralysis was an inherent risk, that can manifest at anytime, reasonable care would not avoid it. The breach did not result in the injury, but the deprivation of autonomy.

"In my opinion this argument is about as logical as saying that if one had been told, on entering a casino that odds in the number 7 coming up at roulette were only 1/37, one would have gone away and came back next week or gone to a different casino, the question is whether one would have taken the opportunity to avoid or reduce the risk, not whether one would have changed the scenario in some irrelevant detail."

In essence Lord Hoffmann believes that we should not be twisting the law of negligence by calling this a breach because we feel the need to grant Mrs C her the compensation she deserves.


Lord Hoffmann's argument can be best understood by reference to mathematical probabilities. In Lord Steyn's judgment the probability of the unfortunate damage happening on the first surgery was 1/100, however the chances of it happening on two consecutive surgeries are (1/100)*(1/100)=1/10,000. The problem is that it would be illogical to calculate the probability of the damage occuring if she was to postpone her surgery as the probability of two consecutive occurrences of the surgery, as in order for the second surgery to occur the first must not have conversely for there to even be a illogically relevant probability for the second surgery the first must have already occurred. In the context of the scenario if the first had occurred the second would not, thus it can only be considered as a postponed first surgery and not two consecutive surgeries, hence the correct probability of the "second" surgery or postponed first surgery remains the same 1/100.