O’Connor was a clinical negligence case where the defendant’s expert seems to have changed their position – at least the defendant’s thought so and applied for permission to call a substitute expert. The application was made at the outset of the trial, some 5 months after it had been clear that the expert had shifted position.
Jackson LJ dismissed the appeal as follows:
51. There are also wider considerations in play. The application for permission to call an additional expert was made at the latest possible stage, namely on the first day of trial. If the judge had granted the application, that would have necessitated an adjournment of the trial with consequential delay and massive extra costs.
52. Following the civil justice reforms of 2013, that is simply not how we do things now. See the majority judgment of the Court of Appeal in Denton v T.H.White Ltd  EWCA Civ 906 . Also – dare I say it – paragraph 89 of the third judgment in Denton is directly pertinent.
53. If the judge had granted the defendant’s application, I imagine that the claimant would have launched an urgent appeal. Even though the issue was one of case management (where judges have a broad discretion) I do not see how a decision to abort a clinical negligence trial on day 1 for the benefit of a dilatory defendant could possibly be justified.
Note that this case concerns a change of expert and not the need to make an application under CPR 35.13 to which, it would seem, that CPR 3.9 and Denton would have been directly applicable.
Jackson LJ’s minority judgment in Denton painted the following picture:
89 … There are many hidden costs flowing from adjournment of the trial: witness statements and reports need updating; fee earners handling the litigation may change with a need for newcomers to read into the case; both legal teams continue to work upon the litigation and so forth. In addition to the increased costs there is wastage of resources. Lawyers, experts, factual witnesses and other busy people who had cleared their diaries to attend the trial (probably cancelling other commitments) will have to clear their diaries yet again for another trial a year later. There is also the continuing strain on the parties to consider. What litigants need is finality, not procrastination. Quite apart from its impact on the immediate parties in Denton , the judge’s order has caused unnecessary delay for many other litigants awaiting their day in court.