A Matter of degree: rethinking risk and proportionality in the tort of negligence

By Jack Harding

In Berent v Family Mosaic Housing and London Borough of Islington [2012] EWCA civ 961, Tomlinson LJ explained that:

“One cannot in this context separate the enquiry as to reasonable foreseeability from the related enquiry what it is reasonable to do in the light of the reasonably forseeable risk”

In the modern law of negligence, it is a trite proposition that a defendant is not liable for harm that was not reasonably foreseeable. From that uncontroversial proposition, however, an unfortunate inference is too often drawn: that foreseeability is the operative criterion, such that once a claimant establishes that some injury of the relevant kind was foreseeable, the defendant’s liability must follow. This article seeks to demonstrate that that inference is wrong. Foreseeability is a threshold, not a touchstone. It admits a claim into the arena in which liability is contested (by establishing a duty to take care), but it does not resolve the contest. The issue of breach of duty – to act with reasonable care –  is the true controlling mechanism, and at its heart lies the concept of proportionality. This is the notion that the reasonableness of the alleged tortfeasor’s action is informed, and may ultimately be determined, by reference to the likelihood of the risk of injury occurring and the seriousness of the outcome.

A review of the case law suggests that there are 4 conceptual errors which may have driven a misunderstanding of the doctrine of risk-based proportionality. They are (1) a misunderstanding about the retrospectivity of the analysis (2) the confusion between likelihood of injury and seriousness of outcome (3) the incorrect focus on antecedent conduct rather than the probability of injury and (4) a failure to assess the standard of care by reference to the particular level of injury suffered by the individual claimant.

Before considering each of these factors, it is useful to consider a very recent illustration of the problem in practice.

Transport for London v Young

In Transport for London v Young and Upitis [2026] EWCA Civ 1095 two cyclists had been injured on a section of the ‘Cycle Superhighway 6’ in Central London. Their complaint was that they had both mistaken a raised section of pale stone kerb constructed by the Defendant for a white line painted on the road, believing that they could ride over it. The purpose of the kerb was to separate the cycle lane from the carriageway for the protection of cyclists. Double red lines marked the edge of the carriageway adjacent to the kerb. There was evidence that 5 cyclists in total (including the Claimants) had suffered similar accidents over a period of several years. In the design phase of the cycle way, the Defendant’s road safety audit team had expressed concern that the raised kerb might not be sufficiently visible. It was suggested that reflective ‘wands’ and tapered road markings might be used to address this concern. This was considered by the design team and rejected on the basis that the double red lines provided sufficient demarcation and that kerbs of this nature were common throughout London and a recognised feature of cycle infrastructure. Although it was accepted that reflective wands would mitigate the risk, they were expensive to maintain, since they were prone to be struck by vehicles.

The trial judge found that the Defendant’s approach at the design stage was reasonable. He stated:

“A cyclist who noticed neither the double red line nor the triangle would be a cyclist who was simply not paying attention.”. However, following the occurrence of accidents, which were both ‘reasonably forseeable’ he concluded that it would have been a reasonable, and economic, step to install wands.

The Court of Appeal (Yip LJ giving judgment) held that the judge had elided the duty to act (which arose from the positive act of creating the kerb which created a forseeable risk of injury) with the issue of breach. He had failed to carry out an evaluative assessment of other factors, and in particular the degree of risk in the context of the nature and purpose of the cycle path. Her Ladyship explained, at paragraphs 58 and 59, that:

“Having clearly identified the duty and standard of care at [124], the judge should have gone on to conduct the required evaluative assessment applying that standard. However, at various parts in the judgment, he revisited the duty and in doing so misdirected himself. He repeatedly returned to the question of foreseeability of harm in the context of considering whether the respondent was in breach of duty. In identifying the standard of care (at [125] and [135]), the judge referred to steps to mitigate the risk “so that it was no longer reasonably foreseeable”. He was wrong to do so. The duty owed to cyclists (including those who were less careful than others) was clear as was foreseeability of the risk of harm. But that was not sufficient in itself to require that the respondent should take the measure of installing wands which the judge had identified.

In my judgment, the judge moved too quickly from foreseeability of harm to the availability of a further precaution to his finding of breach. He did not sufficiently explain why the risk, assessed against the high volume of use, the design purpose of the stepped cycle track, the applicable guidance, the prior audit consideration and the consequences of a barrier solution, made it unreasonable for the respondent not to take the further step identified”

The inadequate consideration of the degree of risk was perhaps most apparent in the judge’s consideration of the previous accidents. As Yip LJ explained at paragraph 55:

“The accident history was also material. A very large number of cyclists used the route. The fact that a small number of accidents occurred does not of itself establish that the risk was so substantial that further precautions were required. Equally, the absence of a long history of accidents is not conclusive, particularly where safety audits had identified the possibility of confusion. The point is that the judge had to engage with the scale of the risk in proportion to the use of the route and explain why that risk crossed the threshold requiring further mitigation. The judge’s treatment of that point was limited. He merely distinguished the facts of this case from those in Tomlinson and other cases without engaging in proper consideration of the principle that the degree of risk is a factor to be weighed separately from the potential seriousness of outcome. It was highly relevant in considering the proportionality, and therefore reasonableness, of any response”

Having concluded that the judge had fallen into error, the Court of Appeal remitted the case back to the County Court for a reconsideration.

In order fully to understand where the trial judge went wrong in Young, an analysis of the 4 common misunderstandings about the concept of risk is required.

Retrospectivity

In Hart v Lancashire and Yorkshire Railway Company [1869] 21 L.T. 261, Bramwell B memorably stated:

“…people do not furnish evidence against themselves simply by adopting a new plan in order to prevent the recurrence of an accident. I think that a proposition to the contrary would be barbarous. It would be, as I have often had occasion to tell juries, to hold that, because the world gets wiser as it gets older, therefore it was foolish before.”

Notwithstanding the striking language used by his lordship, the jurisprudential importance of the point made cannot be overstated in the law of negligence. It is fundamental to a cause of action based on a culpable state of mind (as distinct from a strict liability) that the adequacy of any response to a risk must be determined by looking prospectively through the eyes of the reasonable person in the prevailing circumstances as they existed at the time, rather than with the unlimited wisdom of hindsight.

The point arose for consideration by the High Court of Australia in Vairy v Wyong Shire Council [2005] HCA 62.  Mr Vairy suffered severe, permanent spinal injuries after executing a shallow dive into the sea from a natural rock platform at Soldiers Beach, a popular surfing location. The trial judge found that the risk that a person might sustain severe injury in diving from the platform was forseeable, and neither a far-fetched nor fanciful possibility. She concluded that the erection of warning signs would have been inexpensive and was a reasonable and necessary response to the forseeable risk. This finding was overturned on appeal to the Court of Appeal, whose judgment was upheld by the High Court. The correct approach to the analysis of risk was considered in detail by Hayne J (emphasis added)

“Because the inquiry is prospective, it would be wrong to focus exclusively upon the particular way in which the accident that has happened came about. In an action in which a plaintiff claims damages for personal injury it is inevitable that much attention will be directed to investigating how the plaintiff came to be injured. The results of those investigations may be of particular importance in considering questions of contributory negligence. But the apparent precision of investigations into what happened to the particular plaintiff must not be permitted to obscure the nature of the questions that are presented in connection with the inquiry into breach of duty. In particular, the examination of the causes of an accident that has happened cannot be equated with the examination that is to be undertaken when asking whether there was a breach of a duty of care which was a cause of the plaintiff’s injuries. The inquiry into the causes of an accident is wholly retrospective. It seeks to identify what happened and why. The inquiry into breach, although made after the accident, must attempt to answer what response a reasonable person, confronted with a foreseeable risk of injury, would have made to that risk. And one of the possible answers to that inquiry must be “nothing”

If, instead of looking forward, the so-called Shirt[1] calculus is undertaken looking back on what is known to have happened, the tort of negligence becomes separated from standards of reasonableness. It becomes separated because, in every case where the cost of taking alleviating action at the particular place where the plaintiff was injured is markedly less than the consequences of a risk coming to pass, it is well nigh inevitable that the defendant would be found to have acted without reasonable care if alleviating action was not taken. And this would be so no matter how diffuse the risk was – diffuse in the sense that its occurrence was improbable or, as in Romeo, diffuse in the sense that the place or places where it may come to pass could not be confined within reasonable bounds.”

Although the Court of Appeal did not address the point directly in in Transport for London v Young, it is arguably the case that the trial judge fell into the same error. Having concluded that the accident would have been avoided if wands had been installed, it was an easy step to link this back to the forseeable (and indeed, foreseen) risk of accidents, and therefore to conclude that liability was established. By failing to carry out an evaluative assessment of other factors, and in particular the degree of risk, his analysis was more akin to the sort of factual inquiry into the causes of the accident and how it could be avoided, as explained by Hayne J in Vairy, above.

The seriousness of the outcome

Many of the cases in this area of law involve catastrophic injury of the most serious nature. It is unsurprising that the Courts should be deeply sympathetic to the Claimants. At the heart of every claim is a person whose life has been changed, more often than not irreparably so. However, it is clear that sympathy for the individual cannot be a basis for finding liability in a principled system of law.

Stripped back, a similar point arises in the context of the present discussion on risk, namely that the seriousness of the injury sustained cannot be divorced from whether the injury was likely to occur in the first place. In Tomlinson v Congleton [2004] 1 AC 46 Lord Hobhouse expanded on this principle with customary eloquence:

“The second point is the mistreatment of the concept of risk. To suffer a broken neck and paralysis for life could hardly be a more serious injury; any loss of life is a consequence of the greatest seriousness. There was undoubtedly a risk of drowning for inexperienced, incompetent or drunken swimmers in the deeper parts of the mere or in patches of weed when they were out of their depth although no lives had actually been lost. But there was no evidence of any incident where anyone before the claimant had broken his neck by plunging from a standing position and striking his head on the smooth sandy bottom on which he was standing. Indeed, at the trial it was not his case that this was what had happened; he had alleged that there must have been some obstruction. There had been some evidence of two other incidents where someone suffered a minor injury (a cut or a graze) to their head whilst diving but there was no evidence that these two incidents were in any way comparable with that involving the claimant. It is then necessary to put these few incidents in context. The park had been open to the public since about 1982. Some 160,000 people used to visit the park in a year. Up to 200 would be bathing in the mere on a fine summer’s day. Yet the number of incidents involving the mere were so few. It is a fallacy to say that because drowning is a serious matter there is therefore a serious risk of drowning. In truth the risk of a drowning was very low indeed and there had never actually been one and the accident suffered by the claimant was unique. Whilst broken necks can result from incautious or reckless diving, the probability of one being suffered in the circumstances of the claimant were so remote that the risk was minimal. The internal reports before his accident make the common but elementary error of confusing the seriousness of the outcome with the degree of risk that it will occur”

His Lordship went on to explain that where the Court confuses likelihood of injury with the seriousness of the outcome, the result may be to impose a standard of care which is disproportionate:

“However, and probably more importantly, the degree of risk is central to the assessment of what reasonably should be expected of the occupier and what would be a reasonable response to the existence of that degree of risk. The response should be appropriate and proportionate to both the degree of risk and the seriousness of the outcome at risk. If the risk of serious injury is so slight and remote that it is highly unlikely ever to materialise, it may well be that it is not reasonable to expect the occupier to take any steps to protect anyone against it. The law does not require disproportionate or unreasonable responses”.

Whilst it is always difficult to detach the analysis of liability from the severity of the injury, it is a necessary function of the objectivity of tort law, and may lead to the conclusion that doing nothing at all is acceptable. As Hayne J explained in Vaile (above):

“Attaching the qualitative description “low”, to the probability of occurrence of the risk, must not be understood as conveying some normative judgment about whether the risk may reasonably be ignored. But the likelihood of occurrence is an important factor to consider. Nor should the use of words like “calculus” be permitted to suggest that what is then required is some mathematical or mechanical analysis. In the end, the question is what response was reasonable? One possible answer is “none was needed”.

Antecedent conduct versus risk of injury

Even where the court has correctly directed its attention to the initial degree of risk rather than the gravity or seriousness of the outcome, a further pitfall potentially awaits. This is the temptation to reason that because an activity occurs with significant frequency, ‘sooner or later’ an injury is, or was, bound to occur, even if it has not already.

This point arose in another Australian case in which the claimant sustained catastrophic injury  diving into shallow water. In Roads and Traffic Authority of NSW v Dederer [2007] HCA 42 the High Court overturned the lower courts’ conclusion that the Defendant had been liable for failing to prevent, or deter, young people, from jumping from a bridge that it owned. The undisputed evidence was that such behaviour was a common occurrence and had been for many years. However, there had been no prior accidents. Gummow J explained why this was a factor of significant importance:

“The first error can be seen in Ipp JA’s characterisation of the “startling frequency” of “large numbers” of people jumping and diving from the bridge; a practice that was “continuing unabated” notwithstanding the pictograms. Such a characterisation incorrectly focused attention on the frequency of an antecedent course of conduct, namely jumping and diving, and not on the probability of the risk of injury occurring as a result of that conduct, namely impact in shallow water. As Lord Porter observed in Bolton v Stone, “in order that the act may be negligent there must not only be a reasonable possibility of its happening but also of injury being caused” (emphasis added). In the present case, the frequency of jumping and diving was only startling if one ignored the fact that no-one was injured until Mr Dederer’s unfortunate accident. Far from being a risk with a high probability of occurrence, the probability was in truth very low, and this fact was masked by the Court of Appeal’s characterisation of the relevant risk.

Again, this conceptual error is likely to be magnified by focusing too closely on the foreseeability and disregarding the degree of risk. Foreseeability is a low threshold. It will often be unrealistic to argue that some sort of accident is not foreseeable in the broadest sense, not least because of the well-established principle that the precise chain of events leading to it need not have been: Hughes v Lord Advocate [1963] AC 837 . However, not every activity leads to an accident, and not every accident results in injury. It is clear that there must be a rigorous process of analysis, moving through the different stages of the factual inquiry, before the court can reach the conclusion that the risk of actual injury, to the claimant in question (not the public at large) was of a sufficient degree that it was reasonable and proportionate to require a response. The need to focus on the individual claimant leads to the final error of reasoning considered below.

The particular injury suffered

In Shaw v British Railway Board [1982] 1 Lloyds’s Rep 322 , the Claimant, a train driver, “bumped” his head while inspecting the engine compartment of the train he was driving in course of his employment, with result that the retina of his left eye became detached and he became completely blind in the affected eye and retired from work. The trial judge found the defendant negligent “in failing to provide the plaintiff with a helmet or other adequate head protection to wear whilst in the engine compartment and in failing to instruct him to wear such helmet when going from driver’s compartment to the boiler compartment or the engine compartment or the brake compartment”.

The Court of Appeal overturned the decision, holding that the judge had failed properly to consider the magnitude of the risk of the particular type of injury sustained occurring:

“He then posed the second of his questions (to which I need not refer) which he also answered in the affirmative. The first and vital question and the answer to it would appear to have left out of consideration an essential factor contained within the test which a duty of care is adjudged to arise. It is the factor which relates to the magnitude of risk. An employer is not expected to take safety precautions without regard to the magnitude and the seriousness of the risk to which he is exposing his workman. There are all manner of incidents which arise in the course of a man’s employment which must cause some kind of injury of a comparatively trivial nature against which an employer is not obliged to afford protection.

…

I content myself with dealing with the seriousness of the injury risked which, with great respect to the learned judge, I think he neglected to have in mind, or fully in mind, when deciding there was a duty owed and a breach of it. It could be said he had it in mind seeing that he commented: “One can visualise other possible injury” . If so, I ask rhetorically: “what other injury could in the circumstances one visualise?” It is not, of course, possible to visualise the extent of injury unless regard is had to the kind of accident which is foreseeable. As I have said already, the whole history of accidents so far as they are known, do no more than inform us that the kind of injury sustained by only several drivers was trivial” (per Stephenson LJ)

This is a principle which applies with equal force outside the context of employers’ liability. Indeed, in any situation in which an activity carries some risk of minor injury, it will often be the case that this is accepted as an unavoidable and acceptable feature of participation. It cannot be used as the basis for imposing liability where a far more serious injury (even of the same type, for example ‘orthopaedic’) occurs. This is because the severity of the actual injury sustained informs the question of what should reasonably have been foreseen in the first place, and what action is reasonably required in response. It is a prime example, in the words of Tomlinson LJ in Berent above, of the need to avoid separating “the enquiry as to reasonable foreseeability from the related enquiry what it is reasonable to do in the light of the reasonably forseeable risk”. If foreseeability and reasonableness of response must considered together, the proportionality of the response must be linked to a risk of the relevant type and degree.

This is best illustrated by the case of Harris v Perry [2009[ 1 WLR 19 . The Defendant parents hired two inflatables, a bouncy castle and a bungee run, for a tenth birthday party for their triplets. Prior to the party, various children were given permission to play on the inflatables, including the 11-year-old claimant and a 15-year-old boy who was much taller than the claimant. The second defendant was supervising the children from a position in front of both inflatables but, at one stage, she went to help a child on the bungee run and her back was turned to the bouncy castle. During that time, three children did one somersault each on the bouncy castle. The claimant did the second of the somersaults but, before he was back on his feet, the 15-year-old boy did a somersault and his foot hit the claimant’s forehead and caused catastrophic injury

The trial judge found in favour of the Claimant without any consideration of the degree of risk. The Court of Appeal overturned this decision. It held that the duty to act with reasonable care was discharged if steps were taken to protect against non-serious injury. It was only if serious injury of the kind sustained was itself specifically foreseeable that liability could be established:

“38…A reasonable parent could foresee that if children indulged in boisterous behaviour on a bouncy castle, there would be a risk that, sooner or later, one child might collide with another and cause that child some physical injury of a type that can be an incident of some contact sports. We do not consider that it was reasonably foreseeable that such injury would be likely to be serious, let alone as severe as the injury sustained by the claimant.

39.  Not only was it not reasonably foreseeable that boisterous play on the bouncy castle would involve a significant risk of serious harm, there was no evidence before the judge, or before us, of the extent of the risk of injury actually posed by bouncy castles. If injuries such as that suffered by the claimant had been suffered by those playing on bouncy castles on even infrequent previous occasions we would expect the risk of such injuries to have been specifically drawn to the attention of those hiring them.

40.  For these reasons, we consider that the standard of care that was called for on the part of the defendant was that appropriate to protect children against a foreseeable risk of physical harm that fell short of serious injury”

In Uren v Corporate Leisure UK [2011] EWCA Civ 66, the Court of Appeal applied a similar approach where an adult claimant sustained serious spinal injury diving into a shallow pool during a ‘fun day’ at a RAF base:

“I will deal first with Sir Geoffrey’s criticism of the judge’s approach to the law. It is said that the judge should have considered the risk of any physical injury and not limited himself to consideration of serious injury by which he meant spinal injury. I do not accept that the judge limited his consideration to spinal injury but, even if he did, this would not, in the circumstances of this case, have been an error of law. It was accepted on all sides that, arising from this game, there was some risk of moderate injury (for example a fracture of the upper limb) and no doubt a variety of trivial injuries too. It was not in issue whether those risks were such that the game should have been stopped or that head-first entry should have been forbidden on account of them. I would have thought that the balance of those risks and the benefit of the game would favour the continuance of the game. But those wider risks were irrelevant to the issue before the judge which was whether the risk of a fractured spine or other serious injury (e.g. to the head) was such that head-first entry should have been banned.”

It is worth noting that when the case was remitted to the High Court for further consideration, the judge found on the facts, that the risk of ‘serious injury’ was indeed forseeable and liability was established.

Conclusion

The Court of Appeal’s recent decision in Transport for London v Young illustrates that a misunderstanding of the concept of risk, and its unifying importance in law of negligence, remains a problem in the present day. It is hoped that by dissecting and considering the different factors which underly this area of law, this article has helped to shine a light on the need for a more rigorous analytical approach to the issue in the future.

[1] A reference to Wyong Shire Council v Shirt [1980] 146 CLR 40, a seminal decision of the High Court which emphasised the need to evaluate factors, including the degree and magnitude of risk, in assessing breach of duty in negligence.