Collyer v Mid Essex Hospital Services NHS Trust [2019] EWHC 3577 (QB) 

This article originally appeared in Issue 4 (March 2020).

The Facts 

The Claimant underwent a planned surgical removal of his larynx in order to treat recurrent laryngeal cancer. There was no disagreement that this was the only appropriate treatment option. However, as a consequence of the procedure, the Claimant suffered nerve damage and lost all movement in his tongue. The parties’ respective experts had been unable to find any evidence in the relevant literature of comparable nerve damage as a complication of laryngectomy: whether following negligence or otherwise. The Claimant sought to rely on the fact of the total absence of reports of such damage occurring to argue that, if the injury suffered is one that does not ordinarily happen if reasonable skill and care is exercised, then since it is not a potential non-negligent complication it must have been caused negligently, and suggested initially that it gave rise to a “presumption of negligence.” 

Causation in law 

The Claimant had not sought to plead that this was a case where the ‘material contribution’ exception to the usual ‘but for’ causation principle could apply. Accordingly, HHJ Coe siting as a judge of the High Court unsurprisingly emphasised that, as the Claimant had the burden of proving his case, even if a court considers that there are a number of negligent and non-negligent possible causes of an injury, nevertheless a Claimant must still establish that the negligent cause he puts forward was not just the most likely but was more likely than not to have been the cause. 

HHJ Coe cited the decision of the House of Lords in Rhesa Shipping Co S.A. v Edmunds and Fenton Insurance Co Ltd [1985] 1 WLR 948 (“the Popi M“) as authority for the principles that a Defendant is not obliged to suggest an alternative cause for injury, or to prove on a balance of probabilities the truth of any particular alternative cause, and that “when considering the burden of proof on a balance of probabilities, common sense must be applied. 

Before a judge can find that a particular event occurred, he or she must be satisfied on the evidence that it is more likely to have occurred than not. If the judge concludes even on a whole series of cogent grounds that the occurrence of an event is extremely improbable, a finding by him that it is nevertheless more likely to have occurred than not does not accord with common sense.”

HHJ Coe also referred to O’Connor v The Pennine Acute Hospitals NHS Trust [2015] EWCA Civ 1244 for the proposition that where there are a number of alternative causes, disproving all the alternatives does not in itself amount to proof of the remaining possible cause as being the effective cause. 


Having analysed the respective expert evidence HHJ Coe concluded that both experts had been forced to identify a possible cause for the Claimant’s nerve damage rather than a likely one. HHJ Coe found that the Claimant had a lack of tongue functioning immediately following the operation, and according the ‘mechanism of injury’ had occurred during surgery. However, when considering which of the four possible mechanisms of injury mooted by the experts had in fact occurred, HHJ Coe concluded in favour of the Defendant as while there were two mechanisms that were remote possibilities/not completely impossible, it was not possible to say on a balance of probabilities that either had in fact been the cause. Accordingly, while unsatisfactory, there was no option for the court but to conclude that the injury remained unexplained. 


This case is a useful reminder that even with all the benefits of medical expert evidence, there may well be cases where it is simply impossible on a balance of probabilities to establish what was the mechanism of injury. It also is another reassertion of the importance of the ‘but for’ causation test – following not long after the judgment in Arksey v Cambridge University Hospitals NHS Foundation Trust [2019] EHWC 1276 (QB) (discussed here) represented a similarly robust assertion of the importance of the ‘but for’ causation test and a further reminder that pleading ‘caused and/or made a material contribution’ is not a ‘get out of gaol free’ card. 

William Edis QC acted for the Claimant in this case. He did not contribute to this article.