Key takeaways
The counterfactual
Must be clearly articulated and precisely pleaded from the outset. It is not for Defendant to fill gaps.
Cauda equina syndrome cases
Claimants must set out clear ‘but for’ timings and nature of intervention, as well as how this interacts with their case on medical causation.
Courts continue to take stand against late amendment of pleadings
Late changes risking trial dates or requiring new evidence and additional work face significant resistance.
The High Court decision in Williams v Wilkinson [2026] EWHC 1088 (KB) provides useful guidance on the importance of pleading a clear case on causation from the outset and in particular considering the counterfactual scenario. The Court refused the Claimant permission to amend and reformulate her case on causation, late in proceedings. The Judgment arose in the context of a cauda equina syndrome (CES) case and highlights the specific importance of addressing the counterfactual in these cases, but the message is equally appliable in other clinical claims.
Williams v Wilkinson [2026] EWHC 1088 (KB) (08 May 2026) was a case which arose from an alleged failure by an osteopath to advise urgent hospital attendance in the light of the Claimant’s red flag symptoms, leading to a delayed diagnosis of CES. Breach of duty was not in dispute, but the Defendant’s case was that surgery would not have arisen any earlier on the counterfactual scenario, and in any event the delay made no material difference to the outcome.
Two months before trial (and after the experts’ joint statements), the Claimant sought to amend her Particulars of Claim and rely on additional expert and witness evidence. It was agreed that this would involve vacating the trial date.
The Claimant’s initially pleaded case was that she would have attended A&E between 18:00 and 18:30 on 14 February 2020, undergoing an MRI scan followed by emergency surgery that evening.
The amended case accepted she would likely not have attended A&E immediately, indicating that she would therefore have come to surgery during the night or by 9:00 on 15 February 2020.
Mr Justice Cotter refused the application, reinforcing the increasingly robust approach by Courts to ’very late’ amendments when exercising their discretion under CPR 17.3.
The overriding objective is a central guide and there is a balancing exercise between injustice to the Claimant and to the Defendant and wider litigants.
The timing of the application is important. A ’very late’ application is one which threatens the trial date and a heavy burden is placed on the applicant. The Court will consider the reasons for the timing of the application, the nature of the amendments and the consequences. It is not sufficient to simply say there is no prejudice.
While Mr Justice Cotter didn’t accept that the amended case was ’bound to fail’, he felt the prospects of success of the reformulated case was very uncertain and something of a ’holding position’; noting that it failed to address key aspects of the counterfactual, for example:
the time it would have taken to arrange a scan
the relevance of the fact that a treating registrar had determined at 05:45 on 15 February 2020 that the Claimant’s surgery could wait until the morning (but “when” that morning had not been investigated) and
the actual surgical priorities on the morning of 15 February 2020 which led to an urgent patient being operated on before the Claimant.
The Judge said: “That the proposed amendment is pregnant with obvious issues that have not yet been addressed is a matter which should properly be weighed into the assessment of whether permission should be granted as it effects the amount of work that will be required in the future and the strength of the new case, which impacts on the degree of injustice to the Claimant if the amendment is not allowed.” (paragraph 81).
Ensuring cases are addressed expeditiously was also key. The Judge found the amendments would radically alter the Claimant’s case such that the Defendant would need time to reassess, obtain further evidence and amend his own case, impacting the Trial date.
The Judge also examined whether there was good reason for the delay applying to amend. It was held that the complexities on causation should have been obvious much earlier, either on receipt of the Defence or after exchange of expert evidence. The Court was also unimpressed by the Claimant’s failure to plead a positive case on causation from the outset, making clear that the Defendant is entitled to meet a case as pleaded and that there is no obligation on a Defendant to incur the costs of investigating and pleading a case which has not been advanced.
The Claimant’s application was refused. This strict approach to late amendments highlights the need for precision and discipline when pleading causation. The Claimant must properly investigate and formulate their case early, carefully addressing the counterfactual, supported by expert evidence. A ’wait and see’ approach to developing causation arguments may not remedied by a late application, particularly where trial is imminent.
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