Serious and catastrophic injury claims inevitably involve some sort of hospital treatment and often surgery. Usually there is no problem following such treatment. However, when something goes wrong the question whether there has been a novus actus which has broken the chain of causation is asked.

The hitherto usual analysis of the circumstances surrounding whether a specifically medical intervention has broken the chain of causation concerns itself with whether a “Specific Rule” operates limiting novus actus to instances where the treatment is so grossly negligent as to be completely inappropriate.

In Jenkinson v Hertfordshire County Council, the defendant appealed a refusal in the County Court of its application to amend its defence. Mr Justice Baker hearing the appeal in the High Court found that there was no such Specific Rule and that the ordinary rules of causation should be applied. In other words the extent of the damage for which the defendant should be held responsible was the key.

The accident and treatment

The claimant (C) suffered a serious ankle fracture when he stepped into an uncovered manhole. The defendant, as the highways authority, admitted liability for breach of its statutory duty but disputed quantum.

C underwent surgery to repair his ankle but it was unsuccessful. C ended up having six further operations over the following three years with amputation being considered at one stage.


Proceedings were issued and the case was listed for a CCMC in April 2022. In March, the defendant (D) had served a medical report from an orthopaedic surgeon, Mr David Machin, in which he said that although the diagnosis, injury assessment and type of surgery proposed had all been appropriate, the surgery itself had been performed negligently. Had it not been, he would have expected C to be able to return to work within three to six months.

At the CCMC, D asked for an adjournment and indicated it would be seeking to amend its defence to join the NHS Trust. The court refused and directions and a trial date were given. D’s application was heard in May 2022 and the district judge (DJ) refused it. D appealed after being given permission.

Novus actus?

D’s proposed amendment in effect pleaded that it could not be held liable for loss and damage resulting from the negligent treatment of the original injury. The DJ had said at the original hearing of D’s application that only medical treatment “so grossly negligent” could break the chain. There was no real prospect of D establishing this and permission to amend was denied.

The judge referred to the inclusion of the rule in Clerk & Lindsell over 20 years and its endorsement in a Court of Appeal case from 2001, Webb v Barclays Bank in which it was held that liability for an injury was not ended by the negligence of any intervening doctor unless that negligence was so gross as to break the chain of causation.

He also referred to another Court of Appeal case, decided in 2000, Rahman v Arearose Ltd, and noted that the court there had no need of a rule in which gross negligence was the key to deciding liability. Indeed the NHS Trust in Rahman conceded it had sole responsibility for the claimant’s right-sided blindness without there being any finding of gross negligence. This concession was correct in the circumstances but, had there been a “Specific Rule”, such a concession could not have been correct.

Without the Specific Rule there was a real chance, according to Mr Justice Baker, of Mr Machin’s opinion being accepted i.e. C’s injury was so badly treated that D should not be held responsible for its consequences. As the judge put it, a fracture repair that fails within a few days might be found, after a trial, not to have amounted to a fracture repair at all.

Ultimately, Mr Justice Baker found that permission to amend should have been given in the first place and that the court below was wrong to have decided matters on the premise that such a Specific Rule existed:

“In my judgment, the Specific Rule does not exist as a principle of law defining a necessary ingredient of a novus actus defence in the context of medical interventions.” (para 43 of the judgment)


It remains to be seen whether this decision marks a new dawn for the novus actus defence or whether it is an anomaly.

Mr Justice Baker only considers whether the novus actus defence is arguable rather than whether it is actually established. A low bar has been passed but a much higher bar remains and this decision, of course, does not prejudge the issue or mean that the case against the Trust would necessarily be successful.

We also question whether this decision affects the landscape between a tortfeasor and another potential defendant given the well-established principles surrounding contribution claims and apportionment between defendants, principles which will be unaffected by this decision.

Nevertheless, the decision offers a challenging analysis of a causation defence, which many had thought was largely irrelevant to all but a handful of cases, and may help provide defendants with more powerful arguments with which to reduce their potential liability in cases where another person might have caused harm to a claimant.