Pearce v East and North Hertfordshire NHS Trust  EWHC 1504 (QB) (11 June 2020)
This is an application by D to amend the Defence in this action for damages for personal injury arising from clinical negligence. The application is contested on the grounds that the application is made very late and, if granted, would require the trial to be vacated; that there is no good reason for the late timing of the application and the amendment raises an argument which, in the context of this claim, carries no realistic prospect of success. 
CPR 17.3 which confers on the Court a broad discretionary power to grant permission to amend. The case-law is replete with guidance as to how that discretionary power should be exercised in different contexts...
a) In exercising the discretion under CPR 17.3, the overriding objective is of central importance. Applications always involve the court striking a balance between injustice to the applicant if the amendment is refused, and injustice to the opposing party and other litigants in general, if the amendment is permitted.
b) A strict view must be taken to non-compliance with the CPR and directions of the Court. The Court must take into account the fair and efficient distribution of resources, not just between the parties but amongst litigants as a group...
c) The timing of the application should be considered and weighed in the balance. An amendment can be regarded as 'very late' if permission to amend threatens the trial date...
d) The prejudice to the resisting parties... The risk to a trial date may mean that the lateness of the application to amend will of itself cause the balance to be loaded heavily against the grant of permission. If allowing the amendments would necessitate the adjournment of the trial, this may be an overwhelming reason to refuse the amendments.
e) Prejudice to the amending party if the amendments are not allowed will, obviously, include its inability to advance its amended case, but that is just one factor to be considered. Moreover, if that prejudice has come about by the amending party's own conduct, then it is a much less important element of the balancing exercise. 
I refuse to allow D to make the amendment sought. The inevitable need to adjourn the trial coupled with the failure to supply any good explanation for the need for the amendment and the lateness of the application drive me to the conclusion that the balance of prejudice tips heavily in favour of refusal. 
I also bear in mind that in refusing the application I am depriving D of running a causation argument at trial. On the basis of the information currently available, it is not possible for me to fine-tune my evaluation of the merits of the amendment further than to record that I am unable to conclude that it has no merit or only a fanciful prospect of success. However, even if I had concluded that the amendment raised a strong defence on causation, I would still not have allowed the amendment. Any prejudice to D in being deprived of running the argument is neutralised by the fact that D has brought the situation upon itself and for no good reason.