In this article, Justin Valentine examines the concept of material contribution focusing on its application to clinical negligence litigation subsequent to the important Court of Appeal case of Holmes v Poeton. He argues that the analysis of Ritchie J in CNZ v Royal Bath Hospitals is, in some respects, to be preferred to that in Holmes and that Ritchie J’s judgment declining to apportion damages on the basis of “functional” indivisibility is, in effect, merely an application of the material contribution principle. He suggests that further judicial consideration of material contribution is highly likely, particularly in relation to cases where the same injury would have occurred absent negligent causes. He concludes with practical advice as to how and when to make allegations of material contribution in clinical negligence cases.
Introduction
As acknowledged by Stuart-Smith LJ in Holmes v Poeton Holdings Limited [2023] EWCA Civ 1377 material contribution is an area of law “That has been bedevilled by apparent inconsistency and imprecision at the highest level on multiple occasions.”.
In such a complex area, a full discussion of material contribution would require some kind of archaeology of previous case law (as the Court of Appeal partly did in Holmes) which by necessity requires in-depth knowledge of that case law and familiarity with the shifting terminology. On the other hand, an attempt can be made to explain what the law now appears to be following Holmes along with some observations as to what the future developments may be. I shall, so far as is possible, adopt the latter approach. As a practitioner primarily dealing with clinical negligence litigation, rather than industrial disease, this discussion is focused on clinical negligence.
Causation in tort law
In most personal injury claims where there is a single tortfeasor and a clearly defined and understood mechanism of injury, the issue of causation is straightforward. A car negligently strikes a pedestrian and injury is sustained. An employer negligently fails properly to guard a saw and the employee is injured. In both cases, but for the breach, there would be no injury. Putting it the other way round, if the event (injury) would have occurred irrespective of the breach, then the breach is not a cause of the injury and the “but for” test is not satisfied.
Matters become more complicated in industrial disease and clinical negligence litigation. In industrial disease cases there may be periods of negligent along with non-negligent exposure to a toxic substance or agent whilst an employee was at work. In clinical negligence there are usually multiple causes at play since clinical practice deals with patients who are already injured or ill and the clinical negligence impacts upon a pre-existing treatment pathway, typically there may be poor or delayed treatment of an existing condition. One of the difficulties with material contribution is that the concept arose in industrial disease litigation but is regularly applied in the field of clinical negligence.
Indivisible v divisible injuries
It is useful to establish the rationale for the principle of material contribution. Adapting an example from Professor Jane Stapleton, a legal commentator in this area, in her 2013 article “Unnecessary causes”, consider a bridge which will collapse if more than 10 tonnes is placed upon it. The bridge collapse is equivalent to an indivisible injury which, for the sake of this illustration, could be death, the loss of a leg, a heart attack, something definite and discrete rather than an injury or illness which may differ in its severity (referred to as divisible).
Three lorries arrive on the bridge and each lorry weighs 5 tonnes. If lorry A is parked on the bridge, the bridge stands. If lorry B arrives and parks up, again there is no effect. If lorry C arrives, the bridge collapses. Although the proximate cause of collapse was the arrival of lorry C, each of the lorries contributed to the collapse.
Now imagine that you do not know the weight of the lorries and that only one lorry (whether A, B or C) is the negligent lorry, causatively speaking. The two non-negligent lorries are pre-existing medical conditions. Since the weight of the lorries is not, scientifically, known it is impossible to apply the “but for” test (the negligent lorry might weigh only 2 tonnes, but it might weigh 11 tonnes). There is an evidential gap.
For policy reasons, the Courts have decided that in such cases, where there is an indivisible injury and medical science cannot establish the relative impacts of the negligent and non-negligent causes then the claimant succeeds to the extent of 100%. That is clearly a modification of the “but for” test. Under conventional analysis, where the “weights” of the lorry were unknown, a claimant could demonstrate that there were three causes of the injury (the three lorries) but would not be able to demonstrate that “but for” the negligent cause, injury would not have been sustained, ie the claimant could not satisfy the burden of proof.
In the case of a divisible injury, the above analysis, in this straightforward example at any rate, will be unnecessary. A tortfeasor is liable for that part of the damage that they caused. That is wholly uncontroversial. For example, in a delay in diagnosis of cancer case, the tortfeasor is liable to the extent of the worsened illness not for the whole illness.
The above is summed up in the oft-quoted, and judicially-approved, passage from Professor Sarah Green:
It is trite negligence law that, where possible, defendants should only be held liable for that part of the claimant’s ultimate damage to which they can be causally linked … It is equally trite that, where a defendant has been found to have caused or contributed to an indivisible injury, she will be held fully liable for it, even though there may well have been other contributing causes …
Consistent with the above, in relation to divisible injury, in Holmes, the Court of Appeal referred to Mustill J’s judgment in Thompson v Smiths Shiprepairers [1984] QB 405 (an industrial deafness case):
I see no reason why the present impossibility of making a precise apportionment of impairment and disability in terms of time, should in justice lead to the result that the defendants are adjudged liable to pay in full, when it is known that only part of the damage was their fault. What justice does demand, to my mind, is that the court should make the best estimate which it can, in the light of the evidence, making the fullest allowances in favour of the plaintiffs for the uncertainties known to be involved in any apportionment.
They noted, at paragraph 32, that “These principles for the assessment of causation and proof of loss in divisible diseases have, to my knowledge, never been doubted and are well established”. This is what practitioners do all the time, ie what would the outcome have been absent the negligence? The damages reflect the difference between that outcome and the current situation.
The Court of Appeal in Holmes is therefore clear that material contribution applies to indivisible injuries (and has at a stroke swept away dicta to the contrary both at first instance and in the higher courts). They referred to the analysis of Professor Stapleton and noted the approval of that analysis by the Supreme Court in Financial Conduct Authority v Arch Insurance (UK) Ltd [2021] AC 649 at paras 184-185 which concerns individuals pushing buses over cliffs and such like, ie further examples analogous to the bridge example.
In Holmes itself the claimant sought to attribute his Parkinson’s disease, treated as an indivisible injury, to his negligent exposure to a solvent, trichloroethylene (“TCE”), whilst working for his employer, the defendant. He did not seek to rely on the “but for” test but advanced his case on the basis that the negligent exposure materially contributed to his Parkinson’s disease. In the event, the claimant failed in his argument that the TCE made, as a fact, a material contribution to his development of Parkinson’s disease (and did not even prove that it was capable of so doing). This was fatal to his case. Any further comments made by the Court of Appeal were not necessary for their decision and, strictly-speaking, are obiter.
Bailey v MOD [2009] 1 WLR 1052 is an apposite example of material contribution to an indivisible injury in the clinical negligence field. The claimant was admitted to hospital for surgery to treat a gall stone. She became extremely weak and developed pancreatitis. There was negligent lack of care. After transfer to a renal ward she was given a drink, vomited, aspirated the vomit and suffered a cardiac arrest causing brain injury. The trial judge, Foskett J, found that:
the physical cause of her aspiration and subsequent cardiac arrest was her weakness and inability to react to her vomit [and] there were two contributory causes of that weakness, the non-negligent cause pancreatitis, and the negligent cause, the lack of care and what flowed from that; and … since each “contributed materially” to the overall weakness, and since the overall weakness caused the aspiration, causation was established.
The defendant’s appeal was dismissed with Waller LJ noting, at paragraph 46:
In a case where medical science cannot establish the probability that “but for” an act of negligence the injury would not have happened but can establish that the contribution of the negligent cause was more than negligible, the “but for” test is modified, and the claimant will succeed.
In simple terms, there were two “lorries” the weight of which were not known but which together caused an indivisible injury, cardiac arrest (bridge collapse).
Indivisible v divisible injuries – An ongoing source of confusion
A key question, in light of the above, is how to define indivisibility so that the principle of material contribution is engaged. According to Holmes at para 31:
It is a characteristic of divisible diseases that, once initiated, their severity will be influenced by the total amount of the agent that has caused the disease. By contrast, once an indivisible disease is contracted, its severity will not be influenced by the total amount of the agent that caused it.
In the context of industrial disease this approach is readily understandable. In disease cases there is often a time-based causative element to divisible injury, ie where injury depends on how long the exposure lasted for, such as noise-induced hear loss, hand-arm vibration syndrome, asbestosis, which makes apportionment possible at least on a broad-brush basis. Anything which does not fit into that divisible framework is considered indivisible (similar to the bridge collapse analogy in relation to indivisible injury).
However, this dichotomy (amount of agent increasing severity = divisible versus amount of agent triggering disease but not affecting severity = indivisible) is problematic particularly in clinical negligence cases since although in theory the process of injury may be dose-related, it is not possible to distinguish between aspects of the injury caused by the tortious and non-tortious elements. This is a wider understanding of the concept of indivisibility which, it is suggested, better accords with the underlying, claimant-generous, policy rationale of material contribution. This would suggest that an injury should be called “indivisible” even if its severity is “influenced by the total amount of the agent that caused it.”.
For example, in CNZ v Royal Bath Hospitals [2023] EWHC 19 (KB), the claimant suffered profound hypoxic ischaemia (“PHI”), the cessation of blood flow from the placenta to the fetus causing a lack of oxygen to the fetal brain. The longer the period of hypoxia, the more severe the injury.
At para 367 of CNZ, Ritchie J noted that apportionment of damages can be achieved where injury is divisible (as in Thompson v Smiths Shiprepairers) and therefore held, at para 374:
In my judgment these authorities would support a ruling in the present case that a fair way to apportion the damages in a brain damage cause caused by acute PHI at birth would be by way of a percentage based on the relative durations of the PHI caused by the breach compared to the PHI which would have been suffered in any event.
However, after a lengthy review of further cases, he noted that “none of these cases resolved the issue of apportionment in acute PHI brain damage cases where the functional outcome cannot be apportioned or divided because none of them addressed it head on” and he held at para 391:
In law I consider that the cases I have reviewed above show that if there is a scientific gap making proof of causation of functional outcome, therefore also quantification, impossible in contra-distinction to merely difficult, then the claimant will recover 100% of the damage she has suffered due to the acute PHI so long as the claimant can prove that the breach made a material contribution to the reduced functional outcome which was more than de-minimis. [emphasis added]
In the event he held, at para 404, “that had the 6.5 minutes of negligent delay (range 5-8) … the claimant would have avoided all brain injury.”. Strictly-speaking, his comments on not apportioning are therefore obiter.
Ritchie J’s analysis, in the terms of the bridge analogy, would perhaps be to consider a multi-carriageway bridge which carries road traffic, rail traffic as well as a host of other utilities (electricity cables, gas etc). Both the negligent and non-negligent lorries have caused a partial collapse of the bridge (damage to the brain). It is clear what the overall damage is but far from clear which lorry caused which damage (and two lorries may both cause the same or overlapping damage). Ritchie J called this indivisibility of functional outcome (though to be clear, he did not use the bridge analogy).
It is, it is suggested, difficult to understand on policy grounds how this differs from the simple bridge analogy where all the lorries contribute to the same, indivisible, damage. If policy reasons lie behind awarding 100% of the damages to cases where medical science cannot establish whether the “but for” test applies but can say that the tortious cause materially contributed to the overall damage, what difference is there when it is clear that even non-negligent reasons would have caused some damage but medical science cannot establish which damage (so we know what to deduct)?
The reason Ritchie J was forced to devise this principle of indivisibility of functional outcome was the implication in the case law that once an indivisible injury is triggered, the relative contributions of the tortious elements to that trigger cannot be established (like in the simple bridge example). In CNZ the negligent “dose”, on the counter factual case (bearing in mind he found the “but for” test established anyway), could be ascertained (negligent minutes of hypoxia versus non-negligent minutes) but the damage that the negligent dose would cause could not.
It is suggested that CNZ, should be viewed as a conventional application of the material contribution principle dressed up as indivisibility of “functional” outcome. Perhaps part of the problem is an over-emphasis, in the industrial injury cases, on the process of injury (the longer the period of toxic substance or agent, the worse the extent of injury) when all that is required for the principle to apply is acknowledgement of indivisibility of outcome.
At first sight, this contention contradicts the observation in Holmes, cited above, that “once an indivisible disease is contracted, its severity will not be influenced by the total amount of the agent that caused it” since clearly, the longer the hypoxia, the greater the extent of injury. In this passage, the Court of Appeal in Holmes adopts a narrow definition of indivisible injury.
It is suggested that the observation that the hallmark of an indivisible injury is that “its severity will not be influenced by the total amount of agent that caused it” is not consistent with Bonnington Castings v Wardlaw [1956] 1 AC 613. Bonnington Castings dealt with a divisible injury (pneumoconiosis) which was treated by the House of Lords as indivisible (thereby sowing the seeds for subsequent confusion).
Helpfully, the Court of Appeal at paragraph 54 in Holmes provides an analysis (in the context of McGhee) consistent with the above suggestion that what is important is indivisibility of “functional” outcome and not that “its severity will not be influenced by the total amount of agent that caused it”:
To my mind, this indicates that the Bonnington principle had been and was directed to a case where the tortious exposure contributed to the onset of the disease and not its severity. That is at least consistent with the observation of Lord Simon at page 7H that the consultants had not gone so far as to say that washing after work would have made it more probable than not that the appellant would have escaped dermatitis, with no suggestion that the case was concerned about the recovery of damages for part only of the consequences of the dermatitis; and the restatement of the Bonnington principle by Lord Simon at page 8C-D. And, at page 11G Lord Simon said that “a factor, by itself, may not be sufficient to cause injury but if, with other factors, it materially contributes to causing injury, it is clearly a cause of injury” (emphasis added). As with the passage from the speech of Lord Reid at page 4C-E cited above, this is not the language of divisible injuries. [emphasis added]
It is perhaps of concern that the Court of Appeal in Holmes apparently adopts two conceptually discrete definitions of when a disease is indivisible for the concept of material contribution to apply and it is suggested that the analysis at paragraph 54 should be preferred since this analysis is more consistent with the policy principle, with Bonnington and with broader case law, particularly clinical negligence cases.
Further support for the contention that what is important is indivisibility of functional outcome can also be found from consideration of Williams v Bermuda [2016] UKPC 4. The injury to the patient’s heart and lungs was, according to Holmes “treated [by the Privy Council] as an indivisible injury”. However, the injury was caused by sepsis which is a process, para 41 of the judgment in Williams specifically notes that:
In the present case the judge found that injury to the heart and lungs was caused by a single known agent, sepsis from the ruptured appendix. The sepsis developed incrementally over a period of approximately six hours, progressively causing myocardial ischaemia. (The greater the accumulation of sepsis, the greater the oxygen requirement.) The sepsis was not divided into separate components causing separate damage to the heart and lungs. Its development and effect on the heart and lungs was a single continuous process, during which the sufficiency of the supply of oxygen to the heart steadily reduced. [emphasis added].
If the sepsis had gone on even longer, then the injury would have been even worse. The issue, rather, is the impossibility of dividing the separate components causing separate damage. This case therefore appears to be similar to the rationale of Ritchie J’s conclusion in CNZ, ie it is impossible to distinguish negligent from non-negligent damage caused by hypoxia in relation to the outcome.
Consider, by way of a further example, John v Central Manchester and Manchester Children’s University Hospitals NHS Foundation Trust [2016] 4 WLR 54 where the claimant recovered all his damages ie his injury was treated as indivisible not divisible. Dr John suffered a head injury in a fall. There was negligent delay in arranging a CT scan. Common-sense would suggest that brain injury resultant upon raised intra-cranial pressure would be dose-related (analogous to profound hypoxic ischaemia in CNZ) and therefore divisible in terms of its severity. At para 101, Picken J held (with reference to quantification in industrial disease cases):
In contrast, the Bailey and Williams cases are cases where it was impossible, not merely difficult, to attribute particular causes to particular loss. The present case likewise entails impossibility rather than simply difficulty. As such, it is not an appropriate case for an apportionment exercise of the sort advocated by Mr Kennedy [counsel for the defendant]. [emphasis added].
There was no discussion as to whether the injury was divisible or indivisible but in light of the foregoing discussion, it is suggested that it should be treated as indivisible, ie cannot be divided for quantum purposes.
The risk of over compensation
According to Underhill LJ at para 124 in Holmes “in the case of an indivisible injury a tortfeasor who makes a material contribution to the injury is liable for the whole”.
Even more emphatically Stuart-Smith LJ noted, at para 63 that:
… we are bound in the light of Bailey to find that the Bonnington “material contribution” principle applies to cases of indivisible injury and that, where the principle applies, the claimant does not have to show that the injury would not have happened but for the tortious exposure for which the defendant is responsible. [emphasis added].
This cannot be a correct statement of the law (nor what was intended by the Court of Appeal). Can it be suggested that in Bailey if the medical evidence was such that it was proved that the same injury would have occurred due to claimant’s non-negligently weakened state, she would still have recovered in full?
To utilise the bridge example again, if we know that there are 10 lorries all weighing between 1 and 10 tonnes and that the bridge would inevitably have collapsed, the one negligent lorry would be sufficient for a claimant to recover in full notwithstanding that the negligent lorry would have materially contributed to the collapse? Or to utilise a delay in cancer case, if we know that the delay worsened the cancer and quickened the death (and therefore materially contributed to that death) but that the expert evidence is that the patient would in any event have died (though later), it surely could not be suggested that the claimant should recover all the damages from her relative’s death.
Perhaps more accurately, Stuart-Smith LJ, also observed, at para 20 of Holmes that:
no question of apportioning liability arises in this case since no causative contribution has been shown. For similar reasons, although the prospect was raised by the Court during the hearing, this is not a case which involves oversubscribed causes. These important and difficult questions should therefore be left alone until a case in which they actually arise. [emphasis added].
Oversubscription in this context, precisely addresses the point as to the injury which would result from the non-negligent causes. It cannot have been the Court of Appeal’s intention to change the law to such an extent that even where we know the outcome would have been the same but there is material contribution a claimant recovers the entirety of the damages. Further clarification will inevitably be required. The Court of Appeal has, accordingly, “kicked the can down the road” and Holmes can only be viewed as a further development of the law in relation to material contribution and the damages that should follow.
Practical points
Material contribution is a principle that does not apply to all, or even most, clinical negligence cases which will still be advanced on conventional “but for” grounds. The principle is discussed far more than it needs to be. This disproportionate focus is perhaps a reflection of the parlous state of the case law. Although Holmes has improved matters somewhat, it has by no means clarified all the issues and, it is suggested, has failed to reconcile the different, and arguably more nuanced, approach evident in the clinical negligence case law.
In many cases, material contribution is alleged as a sort of a fall back position if there is concern that the conventional “but for” argument will not succeed. This, it is suggested, is a misapplication of the principle. Pleadings that allege “The injury was caused or materially contributed to by the negligence of the defendant” should accordingly be avoided.
A claimant must still prove that injury has been sustained and if it appears that non-negligent causes would be sufficient to cause the entirety of indivisible injury (such as death), then the claim cannot proceed (save for the possibility of additional suffering and shortened life expectancy). This will not be new to clinical negligence practitioners.
Where material contribution may assist is in relation to injuries where the outcome may be indivisible, ie where it may, or may not (as in Bailey) be possible, theoretically, to distinguish between negligent and non-negligence causes in terms of the process (or dose) of injury (such as in CNZ, Williams and John) but that in terms of functional outcome, apportionment would not just be difficult but impossible. In such cases, the claim can be advanced on the basis of 100% recoverability and the claimant can wait and see whether a defendant asserts otherwise. The fall back position in that eventuality would be recovery of a portion of the damages, that related to the tortfeasance, not the loss of the case.
If, on the other hand, the injury is divisible (in terms of outcome) then the claim will be advanced in the usual way on the basis that the tortfeasor is liable for that portion of the damages caused by the negligence. Again, clinical negligence practitioners habitually deal with cases of this type.
There is an argument that as part of the law of causation, material contribution need not be specifically pleaded (beyond the usual pleading as to causation). However, it is suggested that clarity as a party’s case in relation to material contribution would assist in narrowing the issues.
It would also perhaps be sensible to record, both in pre-action correspondence and pleadings, that depending on the development of the expert evidence in the case or further clarification as to the law, the party’s case as to material contribution may have to be reviewed. It may also be prudent to note that a party’s case as to material contribution may depend on findings of fact not yet made by the judge and in this regard the Court of Appeal noted at paragraph 52 of CDE v Surrey and Sussex Healthcare NHS Trust [2023] EWCA Civ 1330 that “I understand the concern of the defendant that the case, as now formulated, was not specifically before the judge at trial [but that] It was not until the judge made specific findings that either party knew with certainty the factual basis for breach of duty and for factual and medical causation.”
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