Aggregation in the context of medical negligence considered by the Commercial Court

United KingdomScotland

The Commercial Court has considered whether claims against a private hospital arising out of the medical malpractice of a consultant breast surgeon could be aggregated as two separate sources or original causes under an insurance policy taken out by the private hospital, Spire Healthcare.


Ian Paterson was a consultant breast surgeon who practiced at two private hospitals operated by Spire Healthcare. Mr. Paterson carried out so called “cleavage sparing mastectomies” leaving behind breast tissue and causing an increased risk of cancer recurring. Separately, Mr. Paterson also carried out unnecessary surgeries on patients where there was no clinical indication for such surgery.

Around 750 former patients of Mr Paterson commenced proceedings against Spire in respect of these two categories of surgeries. Spire entered into a confidential settlement with the patients in 2017. Spire’s outlay on damages, Claimant costs and its own defence costs amounted to over £37 million. Spire sought to recover this outlay under its insurance policy underwritten by RSA, which included a limit of £10 million for all claims “consequent on or attributable to one source or original cause…” subject to an aggregate limit of indemnity of £20 million.

The key issue between the parties was whether the claims against Spire were “consequent on or attributable to” two separate sources or original causes or whether the claims should all be aggregated as attributable to a single source or original cause.

Spire’s submissions

Spire contended that there were two separate groups of claims, each of which were consequent on or attributable to a separate source or original cause and that Spire was subsequently entitled to two limits of indemnity of £10 million.

The two separate groups identified by Spire were:

  1. Claims resulting from the negligent performance of mastectomies, where a mastectomy was clinically indicated but where breast tissue was negligently left behind, causing an increased risk of the recurrence of cancer; and
  2. Claims resulting from unnecessary surgeries that were carried out where such surgery was not clinically indicated.

Spire maintained that it had incurred liabilities and defence costs in excess of £10 million, in respect of each of the two groups and was consequently entitled to recover a total of £20 million under the policy.

RSA’s submissions

RSA accepted that Spire was entitled to an indemnity under the insurance policy in respect of Spire’s legal liabilities to the patients and its defence costs. However, RSA maintained that there was only one source or original cause giving rise to the claims against Spire and RSA was therefore only liable to pay one limit of indemnity of £10 million, which it had already paid to Spire.

RSA argued that Spire drew a false distinction between the negligently carried out mastectomies and the unnecessary surgeries. RSA maintained that all the claims against Spire should be aggregated under a single source or original cause which they identified as “Mr Paterson and his conduct”.

To support its case, RSA argued that:

  • Both groups of claims identified by Spire were pleaded by the patient claimants as having been caused by Mr Paterson’s negligence and the patient claimants who had sent letters of claim to Spire had relied exclusively on negligence;
  • The distinction between the negligent mastectomies and the unnecessary surgeries was a false one as some patient claimants underwent both negligent mastectomies and unnecessary surgeries; and
  • The negligent mastectomies were performed deliberately, just as the unnecessary surgeries had been, as could be seen from the fact that Mr Paterson continued to carry out the negligent mastectomies even after he had assured Spire that he would no longer perform them. Thus, both groups of claims identified by Spire were attributable to the deliberate misconduct of Mr Paterson.

High Court Decision

HHJ Pelling QC, sitting in the High Court, found in favour of Spire, holding that the negligent mastectomies and unnecessary surgeries constituted two separate groups of claims that were consequent on and attributable to two separate sources or original causes under the policy.

Following case law in the area, the Court considered that the standard aggregation language of “claims… consequent on or attributable to one source or original cause..” required that:

  • The widest possible search for a unifying factor in the history of the losses it sought to aggregate;
  • The doctrine of proximate cause should not apply and that losses should be traced back to wherever a common origin could reasonably be found;
  • The words “original cause” should not be construed at such a generalised level so as not to be useful in the context of the search for an original cause;
  • There must be a causative link between what is contended to be the originating cause and the loss and that there must be some limit of remoteness that is acceptable;
  • The search for a unifying factor is a search for why something had happened; and
  • Where a single inpidual operates under two separate mis-appreciations or decisions each resulting in negligent acts or omissions giving rise to multiple claims, each mis-appreciation or decision can be a separate originating cause, even though only one inpidual was involved. If this was not the case, there would not be an effective causal link between the originating cause and the loss in each case, nor would it explain why the negligent act or omission occurred.

Causal link

The need for a causal link between the source or originating cause was underlined by the policy wording which required the claims to be “consequent on or attributable to” the source or original cause. On RSA’s construction of the source or original cause as being Mr Paterson’s negligent and/or deliberate conduct, the causal link between the source or original cause and the loss was missing as it did not sufficiently explain why the loss occurred.

The Judge considered that there were clear causative differences between the negligent mastectomies and unnecessary surgeries. The negligent mastectomies were carried out when a mastectomy was clinically indicated, the procedure was performed negligently, exposed the patients to the risk of recurrence of cancer and was carried out both in the NHS and private practice. The two possible explanations for this conduct were either that it was the consequence of careless and rushed surgery or that it was done for misconceived cosmetic reasons. There was no indication that it was performed for financial gain.

These features were missing in the unnecessary surgeries which were carried out where the surgery was not clinically indicated, did not expose the patients to the risk of the recurrence of breast cancer and was carried out almost exclusively in private hospitals. The likely explanation for this strand of conduct was financial gain.

It could not be said that the mis-appreciation in respect of the negligent mastectomies was causative of the unnecessary surgeries and vice versa.

Legal classification and the existence of mixed claims

The Court dismissed RSA’s argument that the distinction between the two groups was false because the patient claimants in each group pleaded their case in negligence. The Judge held that legal classification is immaterial, and that the focus should be on factual causation instead.

The Judge also dismissed RSA’s argument that the existence of “mixed claims”, where a patient claimant was subject to both a negligent mastectomy and a separate unnecessary surgery, meant that the two groups could not be distinguished. The Judge considered that one inpidual could fall into both groups having undergone two procedures but that did not mean that the first operation caused the other. Such patient claimants would have one claim in negligence but there would still be two separate actionable losses in respect of each surgery undertaken (i.e. the negligent mastectomy and the separate unnecessary procedure).


This case confirms that the “widest possible search for a unifying factor” for the purposes of aggregation cannot be so wide so as to ignore the need for a causal link. The High Court usefully clarified that losses caused by an inpidual operating under two separate mis-appreciations may give rise to two separate sources or original causes for the purpose of aggregation. However, it is important to keep in mind, as pointed out by HHJ Pelling QC in this case, that any aggregation analysis will always be fact specific for each case.

CMS acted for the successful Claimant, Spire Healthcare Limited, in this case.

Article co-authored by Kristyna Muhlfeitova.