It is not sufficient for an individual to simply have a duty of care and then breach the standard of conduct expected of them - that conduct must also cause the damage that the claimant has suffered. Whilst this might seem simple, many accidents can be tied to multiple causes, and certain situations involve claimants contributing to their own injuries. Take, for instance, a car accident; whilst reckless driving might be one of the causes, perhaps the claimant driver was speeding at the time the accident occurred, or maybe a seatbelt in the car had been incorrectly fitted, worsening the situation? Perhaps the accident shunted the driver into a railing which was damaged by a freak lightning strike earlier in the day - an act of god. To muddy the waters even further, there exist issues of evidence - it is not enough to simply argue in court that a harm might have been caused by the defendant, this must be shown to be true on the balance of probabilities.
Much like the criminal law, tort law uses a ‘but for’ test in order to establish a factual link between the conduct of the defendant and the injuries of the claimant. In other words, the question asked is ‘but for the defendant’s actions, would the harm have occurred?’ If the answer to this question is yes, then causation cannot be shown, and vice versa. The ‘but for’ test constitutes the generally applicable rule when it comes to causation.
A relatively modern description of the test can be seen in Cork v Kirby MacLean Ltd.
Case in Focus: Cork v Kirby MacLean Ltd  2 All ER 402
The claimant was painting the inside roof of a factory. The claimant was working on a narrow platform 23 feet above the ground, with no guard-rails or toe-boards. The claimant had epilepsy, and was aware of this fact; his employers were not. Whilst working, the claimant had an epileptic fit and was killed when he fell from his platform.
When the case came to court, the defendants argued that the cause of death was the claimant’s epilepsy, which it could not be held responsible for. Conversely, the claimant’s estate argued that the cause was a lack of appropriate guard-rails on the platform.
In formulating the but for test, Lord Denning said the following:
"if the damage would not have happened but for a particular fault, then that fault is the cause of the damage; if it would have happened just the same, fault or no fault, the fault is not the cause of the damage."
- Lord Denning, at 407.
And thus, because guardrails would have likely prevented the fall, it was ruled that there was a causal link between the lack of guardrails and the injury to the claimant.
In contrast, Barnett v Chelsea and Kensington Management Committee showcases a failed but for test.
Case in Focus: Barnett v Chelsea and Kensington Management Committee  AC 613
The claimant presented himself at a hospital emergency department whilst suffering from stomach pain and vomiting. He was seen by a nurse, who spoke to a doctor, who told her to send the claimant home and for him to call his GP in the morning. Five hours later the claimant died from arsenic poisoning. However, it was established that had the claimant been seen by a doctor he still would have died from the poisoning - there was nothing that the defendant could have done to save him.
Thus, applying the but for test, the courts established that there was no factual causation - the injury to the claimant would have occurred regardless of the defendant’s conduct.
The All or Nothing Approach and the Burden of Proof
As with many elements of negligence, matters of causation are decided on the balance of probabilities (i.e. 51%). Since the burden of proof rests with the claimant, the onus is on him or her to argue that had the defendant not acted negligently, their harm would likely not have occurred. Thus, if a court finds that there is a 55% chance that a defendant caused a claimant’s harm, they will hold the defendant entirely responsible for the harm.
However, this arrangement can be seen as troublesome from a theoretical standpoint. Take Cork v Kirby MacLean Ltd, facts above; in finding against the defendants the courts are essentially stating that they are responsible for the claimant’s harm, when in fact this might not have been the case. Whilst we know that the claimant fell from the platform, and that guardrails might have prevented the fall, this is by no means guaranteed. It is feasible, for example that the claimant might have fallen from the platform anyway, meaning that the defendant’s negligence would have had no effect on the claimant’s injuries. Nonetheless, the defendants were found liable for the full extent of the claimant’s damages.
This approach can be considered problematic because the courts are essentially treating the defendants as if they were 100% the cause of the claimant’s injuries, whilst in fact it is entirely possible that those injuries would have occurred regardless. The all or nothing approach can be seen as particularly problematic when dealing with ‘lost chance’ cases - these are described in detail in a later section of this chapter.
Specific Rules of Factual Causation
As will often occur when examining real-life cases of negligence, there will often be scenarios in which there are multiple causes of the claimant’s harm. In such scenarios, you should first work out if you’re dealing with concurrent causes (causes which happen at the same time) or successive causes (causes which take place one after the other).
Concurrent cause situations are often described as ‘two hunter problems’, referring to a hypothetical situation in which two hunters in the woods both negligently shoot the same victim at the same time, killing him. Standard causation does not help here, since it is impossible to say which hunter caused the victim’s death. At the same time, it is not satisfactory to have each hunter renounce liability on the basis that had they not been negligent, the other bullet would have killed the victim, and so they could not be described as causing the victim’s death.
Subsequent cause situations are a little different - here, one bullet hits the victim briefly before the other. This raises its own set of problems - primarily, the question of whether the second shooter can escape liability just because he was fortuitous enough to have his victim hurt before his negligent act did some harm.
Each of these situations have their own rules which apply, as follows.
Multiple Concurrent Causes - The General Rule
Where there exists more than one possible cause of an injury or harm, the claimant does not have to show that the defendant’s actions were the sole cause of the injury suffered. Instead, it must simply be shown that the defendant’s actions materially contributed to the harm.
Case in Focus: Bonnington Castings Ltd v Wardlaw  AC 613
The claimant contracted pneumoconiosis (a lung disease) from inhaling minute silica particles during his work in a steel production facility. There were two possible sources of the silica particles: a swing grinder or a pneumatic hammer (both pieces of equipment used in shaping steel).
The defendants, who managed the factory, had a statutory duty to provide ventilation for the swing grinder, but not the pneumatic hammer, but had failed to provide any ventilation for either. This meant that the claimant’s illness could be attributed to two possible causes - the illegally present silica dust from the swing grinder which should have been removed by the fan, but also the dust which would have been present from the pneumatic hammer (this distinction is often referred to as the difference between ‘guilty dust’ and ‘innocent dust’). It was argued by the defendant that the burden of proof rested with the claimant, and because the cause of his injuries was only 50% attributable to the defendant, that the claim should fail. The courts rejected this argument, however - in cases involving multiple concurrent causes of injury, the claimant must only demonstrate that the defendant’s negligence made a material contribution to his injuries. Claimants do not have to show that negligence was the sole cause of their injuries. The claim therefore succeeded.
Whilst Bonnington is relatively straightforward because it only deals with two concurrent causes (and thus is a 50%/50% case), the courts still require the claimant’s injuries to be substantially caused by the defendant’s conduct. See Wilsher v Essex Area Health Authority.
Case in Focus: Wilsher v Essex Area Health Authority  AC 1074
The claimant was a prematurely born infant who required extra oxygen in order to survive. A junior doctor inserted a catheter into a vein, rather than an artery, and this resulted in the claimant receiving too much oxygen, causing retina damage and eventually blindness. However, the claimant’s medical situation was such that there were five different possible causes of the blindness, and it was impossible to ascertain which of the five had actually caused the harm. As such, the courts were left considering a case in which only one out of five potential causes was tortious - in other words, there was a 20% likelihood that negligence was the cause of the claimant injuries.
The courts rejected the claim because of this - whilst the claimant could certainly show that it was possible that the defendants had contributed to his injuries, he was unable to show that this contribution was substantial (indeed, it was far more likely (80%) that there was an ‘innocent’ cause for his injuries.
In summary, it is enough to simply show that a defendant has made a substantial contribution to a claimant’s injuries. However, there is a limit to this principle. Whilst a 50% contribution is enough to bring a successful case, a 20% contribution is not.
Exam Consideration: Unfortunately, the courts shy away from providing strict guidelines regarding how much of a contribution to a harm a defendant must make before a successful case can be brought. This is in part due to the fact that it’s rarely possible to describe such contributions as a sure percentage. Instead, the courts simply look to see whether the defendant’s breach is a substantive cause. Fortunately, we can at least see from Wilsher that a substantive cause is definitely greater than 20%.
Multiple Concurrent Causation - Exposure to Risk
Finally, there exists a line of cases where claimants have been unable to show that their harm has occurred as a result of the defendant’s conduct, but have been able to show that their employer has contributed materially to the risk of an injury occurring. This was the case in McGhee v National Coal Board  1 WLR 1 - the claimant was employed to clean brick kilns out after use. This involved exposure to brick dust, and the defendants did not provide showers in the work place. This meant that the claimant had to cycle home whilst covered in brick dust. After some time working in the brick factory, the claimant developed dermatitis (a skin condition) as a result of exposure to brick dust.
Whilst the defendant was not liable for the exposure to brick dust during the claimant’s usual course of work, the courts held that in failing to provide showers, the defendants had materially increased the risk of the claimant developing dermatitis - he was exposed to the brick dust for far longer than necessary. The claim was therefore successful.
This principle has become important where cases involve multiple illegitimate exposures to a risk. Its application can once again be seen in Fairchild v Glenhaven.
Case in Focus: Fairchild v Glenhaven Funeral Services  UKHL 22
The three claimants had all contracted mesothelioma - a type of lung cancer caused by exposure to asbestos. Mesothelioma can be caused by a single fibre of asbestos, which once embedded in the lung can lay dormant for decades, until it causes a tumour to develop. This tumour itself can lay dormant, and it is only during the last couple of years of the disease that symptoms develop - and by then, it is too late to treat. This means that an individual can unknowingly be fatally exposed to asbestos early on in their career, but then continue to work with asbestos for decades afterwards. Conversely, an individual can work with asbestos for many years without a fatal exposure, and then be exposed in the later years of their career. This has led to legal difficulty - since it is impossible to ascertain exactly when and where an individual was exposed to the single dangerous fibre, it can be difficult to work out who the proper defendant is.
This was the situation in Fairchild - each of the claimants was exposed to asbestos during the course of their careers, but by a number of different employers. This created a problem - the claimants were unable to demonstrate which of the employers had actually caused the fatal exposure, just that one of them did. On balance of probabilities, it was improbable that each individual employer had caused the exposure. For example, consider a situation in which an employee has three different employers - this means that each is only 33% likely to have caused the fatal exposure to asbestos, and so for each individual employer they are unlikely to be the one to have caused the harmful exposure.
The courts applied McGhee to deal with this problem, ruling that as long as each of the claimants could show that an employer had materially increased their risk of contracting mesothelioma (by illegitimately exposing them to asbestos), then they were entitled to claim full damages from that employer.
It should be remembered that the Fairchild decision did not occur in a vacuum - tens of thousands of employees were exposed to dangerous levels of asbestos throughout the 20th Century in situations similar to those of the claimants in Fairchild, and so the decision effectively meant that those individuals could seek compensation.
It is also worth noting a couple of other things about this judgement. Firstly, this did not mean that each employee could claim three times - they were only entitled to claim once for their injury. Secondly, whilst this might appear to punish the singled-out employer more than the others, that employer still had the option of suing the others for their contribution to the exposure, meaning that the cost of compensation could effectively be spread amongst the employers. However, it should be noted this is not a guaranteed scenario, since there exists the potential for a defendant to go bankrupt, leaving the other potential defendants to bear the costs of compensation - although see Barker v Corus below for recent changes to such a situation. So, a breach does not have to be the sole cause of an injury - it is enough for a breach to materially contribute to the risk of injury.
This same principle applies in cases even where the claimant has exposed themselves to asbestos voluntarily, as a matter of self-employment. This can be seen in Barker v Saint Gobain Pipelines Plc  EWCA Civ 545. The claimant was exposed to asbestos for nearly 9 years whilst under the employment of the defendant. For the rest of his 30 year career, the claimant was self-employed, working with asbestos on three different occasions. It was held that Fairchild still applied, and that the defendant was liable for the claimant’s mesothelioma because of the material contribution by the defendant to the claimant’s illness. It should however be noted that a 20% reduction in the claim’s value was made due to the claimant’s own contribution to exposure.
It should be noted that the courts appear to have begun the process of limiting this type of liability due to the fact that it can lead to individual employers being singled out for the activities of their peers. This process can be seen in Barker v Corus UK  UKHL 20. Much like Fairchild, the claimant was an employee who had been exposed to asbestos over the course of his career, and had developed mesothelioma. However, some of the potential defendants had since gone insolvent. The decision before the court was therefore, under Fairchild, could the surviving employers be held liable for the shares of the now-insolvent companies?
The courts ruled, contrary to Fairchild, that each employer was only liable for a percentage of damages in proportion to their contribution to the claimant’s risk. For example, an employer who exposed a claimant to asbestos for 10 years of their 30 year career would only be responsible for one third of the damages. In effect, this meant that the idea of joint and several liability applied in Fairchild was overturned, and instead it was held that the idea of ‘proportionate liability’ applied. This also meant that the share of damages attributed to insolvent defendants was not payable.
However, this decision was not without controversy. There was significant backlash from various groups representing mesothelioma victims, and s.3 of the Compensation Act 2006 has reversed the Barker v Corus position - but only in relation to mesothelioma.
In summary, Fairchild provides the principle that materially increasing the risk of a harm occurring is sufficient to establish causation. This principle was applied in Barker v Saint Gobain Pipelines, even where the employee was partially to blame for their own exposure. Barker v Corus has reversed the decision in Fairchild regarding joint and several liability - instead, the position is one of proportionate liability. The effects of Barker v Corus, however, do not apply to mesothelioma due to s.3 of the Compensation Act 2006.
Exam Consideration: Due to the scale of asbestos exposure, multi-claimant cases involving it are a significant feature of everyday tort law. Because of this, there is a high chance you will encounter problem questions regarding asbestos, and so having knowledge of this series of cases is a boon.
Thus, there are two categories of cases involving multiple concurrent causes of injury. The first is where there are a number of different possible causes for the claimant’s injuries. The rule here revolves around the defendant having made substantive contribution to the injury, as per Bonnington Castings and Wilsher.
The second category are cases in which the defendant has materially increased the risk of an injury occurring, as in McGhee and Fairchild.
Exam Consideration: If a problem question can be solved just by using the ‘but for’ test, then do so! If the problem involves multiple concurrent causes, then you will have to refer to the above cases. In such a situation, the most important thing is that you can accurately describe the rule; this will show that you know the law, even If you encounter difficulty applying it to an unwieldy number of contributing defendants.
Multiple Successive Causes
There also exists a small band of cases involving multiple, successive causes of damage - that is, the claimant is harmed by two sources of damage, one after the other. The primary example here is Performance Cars Ltd v Abraham  1 QB 33. The claimant’s Rolls Royce was struck by a negligent driver. Two weeks prior, however, the claimant was in another accident (also in which the other driver was at fault). The damage from the second collision was such that it caused no additional damage on top of the first collision. The claimant was awarded £75 for the first collision, but did not receive it. The claimant then sought to recover the same amount for the second collision.
The courts ruled that a claimant could not be compensated for the same loss twice. However, the question remained over which of the drivers should be responsible for the damage. It was ruled that in such situations, the former, earlier defendant is liable. Thus, to take the two hunter example, it is only the first hunter who is legally responsible for negligently shooting the claimant dead, not the second (and not both jointly).
Lost Chance Cases
There is also a category of cases which deal with the idea of losing a chance - for example, a claimant might have a disease with a 40% recovery prognosis if it is caught early enough. However, due to negligent misdiagnosis the disease might go unchecked, and become terminal in nature. This claimant would be annoyed to say the least, and would therefore want compensation for losing their 40% chance at recovery. Such situations are referred to as ‘lost chance cases’.
As a general rule, the courts are unlikely to compensate a claimant for the loss of a chance, where the lost chance is less than 50%. This principle is best understood via Hotson v East Berkshire Area Health Authority  AC 750 - the claimant fractured his hip when he fell from a tree that he was climbing. When taken to hospital, he was misdiagnosed, and a lack of proper treatment caused the claimant to develop a hip-deformity. Expert evidence stated that even with a correct diagnosis by the hospital, the claimant had a 75% chance of developing the deformity. In effect, this meant that the claimant was deprived of a 25% chance of not developing a deformity. Whilst the Court of Appeal awarded the claimant 25% of total damages on this basis, this reasoning was rejected by the House of Lords - since there was only a 25% chance that the hospital had caused the injury, this did not satisfy the balance of probabilities.
Exam Consideration: Whilst this might appear very similar to situations above, in which there are multiple causes of harm, the relevant case law is different. The two can be distinguished by asking whether the facts of the case involve multiple, equally likely causes, or whether they involve a loss of a chance of avoiding a harm. This will usually be made clear by reference to medical prognosis or similar.
The rule can also be seen to be applied in Gregg v Scott  2 WLR 268, but regarding chance of survival. The claimant found a lump under his arm, and consulted his doctor. The doctor misdiagnosed the lump as benign, when it actual fact it was cancerous. This caused a nine month delay in the claimant’s treatment, and reduced his chance of survival from 42% down to 25%. Again, the Hotson rule meant that this was not actionable because it was more likely than not that the claimant would have died regardless.
It can therefore be seen that the law regarding lost chances is not without criticism. In Hotson, it was clear that the hospital had made a mistake, and that this mistake turned a possible recovery into a certain lifelong medical condition. Nevertheless, because the hospital’s negligence only robbed the claimant of an unlikely chance at recovery, he was unable to claim damages (even those reduced according to the chance his ailment would have occurred anyway). The problem with the status quo can be seen when the margins are made smaller - consider a situation in which Hotson had a 49% chance of recovering had the hospital properly diagnosed him; he would still be unable to claim, despite the hospital effectively changing his prognosis from a coin flip to certain deformity.
That being said, there is some merit to the Hotson position for claimants. For example: consider if a defendant had a 51% of getting better, but lost this chance due to medical malpractice. Under the Hotson principle, that claimant would be entitled to the full extent of damages, because on balance, they would have got better had malpractice not occurred. If, however, damages were calculated based on the lost chance itself, then this particular claimant would only be entitled to 51% of the total compensation for their harm, since there was a 49% chance the harm would have occurred regardless of malpractice.
Furthermore, the decision in Hotson makes it a lot simpler for the courts to work out the proper amount of compensation to be paid. The status quo means that claimants are either entitled to all of the damages or none (this is a slight oversimplification due to principles like contributory negligence, but the point still stands). If the decision of the Court of Appeal in Hotson were to stand, courts would have to spend significant time and resources working out the probability of certain things happening, down to the single percentage point. In contrast, the current situation means that there is no material difference between losing a 75% percent chance of recovery and losing a 70% chance of recovery - in either situation the claimant would be entitled to full damages for their condition.
Exam Consideration: As you might be able to tell, lost chance cases are often subject to significant judicial discussion. They are therefore more likely to turn up in essay questions (although this doesn’t rule out them appearing in problem questions!). It is therefore important not only that you know the Hotson rule, but also the arguments for and against it.
Vindication of Rights Cases
Although lost chance cases demonstrate the problem with adhering strictly to the all-or-nothing approach to causation, there does exist a slim category of cases in which the courts have been willing to ignore the general rule due to policy considerations. Whilst examples are sparse, Chester v Ashfar provides one.
Case in Focus: Chester v Afshar  3 WLR 927
The claimant was soon to undergo an operation to cure her back pain. The defendant, her doctor, negligently failed to warn her that there was a 1-2% risk of her becoming permanently disabled as a result of the operation. She underwent the operation, and despite the operation being carried out correctly, the disabling complication occurred anyway. The claimant could not show that she would have avoided the operation had she known of the risk, but was able to argue that she would have delayed the operation by some time.
In applying the conventional but-for test, the courts found that they could not help the claimant - she would have likely undergone the operation anyway, and so the doctor’s negligence could not be described as having caused the harm - the risk would still have been run, simply at a later date. Nevertheless, the courts acknowledged the fact that the doctor had done wrong - patients have a right to know what they are consenting to. Lord Hope indicates the rights-based nature of the case:
"To leave the patient who would find the decision difficult without a remedy, as the normal approach to causation would indicate, would render the duty useless in the cases where it may be needed most. […] The function of the law is to enable rights to be vindicated and to provide remedies when duties have been breached. […] On policy grounds therefore I would hold that the test of causation is satisfied in this case."
- Lord Hope, at 87.
They therefore found against the defendant, despite the decision appearing to run contrary to conventional causation.
Exam Consideration: McGhee and Chester are difficult to reconcile, whilst both involves situations in which patients are failed by doctors, it is only in the latter case that the court saw fit to validate the claimant’s rights. This can be considered a symptom of incrementalism - rather than sticking to one set rule, the courts can be seen to take each situation at it comes. When considering novel legal situations, it will be up to you to argue whether the general all-or-nothing approach should apply, or whether there is a particular right which should be protected by tort law, as in Chester.
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