Wilsher v Essex Area Health Authority  AC 1074
Claimant always holds the burden of proving likely causation
An infant was delivered prematurely and shortly after was administered oxygen by a junior doctor, accidentally providing too much. The baby was later diagnosed with a retinal condition, which severely limited his sight. Five potential causes or factors were identified to explain the condition, four relating to his premature birth and the fifth being the junior doctor’s actions.
Whether the health authority for which the junior doctor worked could be held liable for his actions where it could not be definitively stated what the chief cause of the injury was. Moreover, should a junior doctor be held to the same professional standards as a fully qualified doctor. Further, should the burden of proof regarding the potential relationship between the negligent actions and the injuries fall to the claimant or the defendant.
At first instance the Court found the defendant, Essex Area Health Authority, liable for the infant’s injuries, citing McGhee v National Coal Board  1 WLR 1 as laying down the precedent that where there existed a plurality of possible causes, the burden fell to the defendant to prove that their actions had not been the but for or material cause of the injury.
The House of Lords subsequently allowed the defendant’s appeal and overturned the first instance judgment stating that whilst the health authority could be held liable for the junior doctor’s actions as junior doctors owed the same duty of care as a fully qualified doctor, the case of McGhee had been wrongly interpreted at first instance; regardless of the number of potential causes of injury, it always falls to the claimant to establish the likelihood of causation.