The recent High Court decision of Collyer -v- Mid Essex Hospitals Services NHS Trust [2019] EWHC 357 confirms that in a clinical negligence case, the burden is on a claimant to prove their injury was caused by negligent treatment. This case should reassure defendants because it means that they do not have to offer alternative explanations for the injury that occurred.


The claimant underwent a surgical removal of the larynx in 2014 for the treatment of cancer. During surgery, he suffered catastrophic nerve damage resulting in almost no movement in his tongue, loss of speech and difficulty swallowing. The operation had been performed for over 145 years but such an injury was not a reported, let alone, recognised complication of the surgery.

In order to succeed at trial, the claimant had to satisfy the legal test that on the balance of probabilities, the damage had been caused negligently. As the injury is not a recognised complication of the procedure, the claimant argued that the most likely cause was human error which gave rise to a "presumption of negligence" against the surgeon. The maxim of res ipsa loquitur (the facts speak for themselves) was also considered but the judge confirmed that it did not apply here and it has very limited application in cases where each side calls evidence.

The claimant's expert put forward two possible negligent explanations of how the injury had occurred, but the judge accepted neither. The defendant's expert put forward non-negligent theories including pre-existing vulnerability of the nerves due to the claimant's diabetes and/or previous radiotherapy. The defendant's theories were also rejected.

The judge acknowledged that both experts were trying to assist by finding a logical explanation. However, because the outcome of this surgery is unreported and there is almost no experience of it among the profession, "both experts were forced to identify a possible cause rather than a likely one. In doing so...there were flaws in their arguments..." .


Although some theories presented a possibility of how the injury had occurred, none of them met the probability, or "more likely than not", test. The judge accepted the damage had occurred during the surgery but the mechanism of the injury remained unexplained. Consequently, the claimant failed to establish that the surgeon had been negligent and the case was therefore dismissed.


Although the case concerned liability in a clinical negligence context, it offers useful reminders for personal injury cases involving complex causation issues:

  • In cases where claimants develop unusual illnesses, they may attribute those to workplace activities or exposures. It is usual for defendants to put forward, and seek to prove, alternative causes. However, although a plausible alternative cause may assist the defence, it is not required and a case can be defended without explanation.
  • With few exceptions, the onus is on the claimant to prove how their injury or illness occurred. The reality is that there will always be cases where the cause of the injury remains unknown and unfortunately for claimants in that situation, their injuries cannot be compensated.
  • Lastly, experts should not feel compelled to identify possible cause(s) rather than likely ones. They should not be driven to theorising and if they are, they may find themselves exposed to judicial criticism and their credibility weakened.


Laura McMillan

Partner & Director of Advocacy