Breach of duty - Illness and disability considerations

Learning Outcomes

This article examines how the standard of care in negligence is adjusted when a defendant is affected by illness or disability. It outlines the general objective standard and explores the specific modifications applied by the courts in situations involving defendants with physical or mental impairments, including considerations of awareness and foreseeability. Your understanding of these principles will assist you in analysing breach of duty scenarios for the SQE1 assessment and applying the correct legal standards to single best answer MCQs. In particular, it explains how sudden and unforeseeable incapacitation may prevent a finding of breach, contrasts that position with cases where the defendant knew or ought reasonably to have known they were unfit to continue, and clarifies the approach to mental illness where actions remain voluntary. It also covers the distinct standard for child defendants and how courts weigh age, experience and risk in setting that standard.

SQE1 Syllabus

For SQE1, you are required to understand how the standard of care in negligence may be modified to account for a defendant's illness or disability. This involves appreciating the interplay between the objective reasonable person test and the specific circumstances of the defendant, with a focus on the following syllabus points:

• The general objective standard of care in negligence.
• How the standard may be adjusted for defendants with physical illnesses, considering their awareness of the condition.
• How the standard applies to defendants suffering from mental disabilities.
• The standard of care expected of child defendants.
• The key principles established in relevant case law regarding illness and disability affecting breach of duty.
• The distinction between voluntary action and true involuntary automatism, and its impact on breach.
• How knowledge (actual or constructive) of impairing symptoms influences the applicable standard.
• The policy considerations behind maintaining an objective standard while accommodating sudden, unforeseeable incapacity.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. What is the general standard of care applied in the tort of negligence?
2. In Mansfield v Weetabix Ltd, why was the defendant driver found not to have breached his duty of care?
3. True or False: A defendant who is aware they are suffering from a condition that might impair their ability to drive, but continues to drive, will be judged by the standard of a reasonably competent driver unaware of such a condition.
4. How does the standard of care differ for a child defendant compared to an adult defendant?

Introduction

Establishing a breach of duty is a key element in proving negligence. It requires demonstrating that the defendant’s conduct fell below the standard of care expected by law. This standard is generally objective – that of the ‘reasonable person’. However, complexities arise when the defendant suffers from an illness or disability at the time of the alleged breach. The courts have developed specific approaches to determine the appropriate standard of care in these situations, balancing the need to hold individuals accountable with the recognition of limitations imposed by physical or mental conditions. This article explores these modifications to the standard of care. It also explains when the defendant’s condition is legally relevant (e.g., unforeseeable incapacitation) and when it is not (e.g., mental illness where acts remain voluntary), and the different approach taken to children.

The General Standard of Care

The fundamental principle is that defendants are judged by the standard of the hypothetical ‘reasonable person’. This objective test disregards the defendant’s individual idiosyncrasies, such as being inexperienced or clumsy. The courts emphasize consistency and predictability by applying this benchmark across contexts, including road use and everyday activities. For activities requiring skill, the law applies the same objective approach by measuring performance against a reasonable practitioner in that role; in clinical contexts this is reflected in the Bolam/Bolitho approach to breach, while for everyday tasks the general reasonable person standard applies.

Key Term: Standard of Care
The level of care expected by law from a person in particular circumstances to avoid causing harm to others. In negligence, this is typically the standard of the 'reasonable person'.

Key Term: Reasonable Person
A hypothetical individual used as a legal standard to determine whether conduct was negligent. This person exercises average care, skill, and judgment in conduct that society requires of its members for the protection of their own and of others' interests.

The objective nature of this test ensures a consistent benchmark. However, strict application without considering personal circumstances like illness could lead to harsh outcomes. The courts soften that harshness only where the defendant’s loss of capacity was sudden and unforeseeable, or where actions were truly involuntary. Otherwise, illness or inexperience is generally irrelevant to the standard itself. In applying the standard, courts also consider factors such as the magnitude of risk and the practicability of precautions (e.g., Bolton v Stone on likelihood and seriousness of harm; Latimer v AEC Ltd on reasonable steps in response to a hazard).

Physical Illness and Impairment

The courts have considered how physical illness affects the standard of care, particularly in cases involving drivers. A key distinction is often drawn based on the defendant's awareness of their condition.

Unforeseeable or Unknown Conditions

If a defendant suffers a sudden, disabling event of which they had no prior warning and could not reasonably have foreseen, they may not be found in breach of duty. Their actions are judged against the standard of a reasonably competent person who is unaware of suffering from such a condition.

In Mansfield v Weetabix Ltd [1998] 1 WLR 1263, the defendant lorry driver developed a hypoglycaemic state that progressively impaired his functioning without prior warning signs he could reasonably have appreciated. He had minor incidents earlier but no clear indication of a problem he could have recognized and acted on. When he eventually lost control and collided with the claimant’s premises, the Court of Appeal held there was no breach: he was judged as a reasonably competent driver unaware of his condition. Key to the decision was the absence of knowledge—actual or reasonably inferable—that he was unfit to drive.

Worked Example 1.1

David is driving when he suddenly and unexpectedly suffers a severe hypoglycemic attack, causing him to lose control of his lorry and crash into Clare's shop. David had never experienced such an attack before and had no medical history suggesting he was at risk. Clare sues David in negligence. Is David likely to be found in breach of his duty of care?

Answer:
No. Based on Mansfield v Weetabix Ltd [1998] 1 WLR 1263, David would likely not be found in breach. The standard of care is that of a reasonably competent driver unaware that he is suffering from a condition that impairs his ability to drive. As David was unaware of his condition and the attack was sudden and unexpected, his conduct did not fall below this standard.

Known Conditions

Conversely, if a defendant is aware, or should reasonably be aware, of a condition that could impair their ability to perform a task safely, they are generally expected to take precautions. Continuing an activity, such as driving, despite knowing of a potentially impairing condition, may constitute a breach of duty. The standard applied is that of a reasonable person aware of their condition.

In Roberts v Ramsbottom [1980] 1 WLR 823, a driver suffered a stroke, experienced symptoms (confusion, partial impairment), and nevertheless continued driving, causing multiple collisions. The High Court found him liable: once aware (or reasonably ought to have been aware) of impairment, he should have stopped. Awareness is evaluated objectively: if a reasonable person would have appreciated that their faculties were impaired such that they were unfit to continue, persisting in the activity will breach the duty.

Worked Example 1.2

Paul realises while driving that his vision is becoming significantly blurred and he feels unwell. He suspects he might be having a stroke but decides to continue driving for another mile to get home. During this time, he collides with another vehicle due to his impaired vision. Is Paul likely to be found in breach of his duty of care?

Answer:
Yes. Paul became aware of symptoms that should have indicated he was unfit to drive. By continuing to drive despite this awareness, his conduct fell below the standard expected of a reasonable driver aware of such impairing symptoms. This aligns with the principle in Roberts v Ramsbottom [1980] 1 WLR 823, where the driver was found liable because he continued driving after becoming aware of stroke symptoms.

Borderline: signs that should have been noticed

The line between unknown incapacitation and known impairment depends on what the defendant actually perceived or ought reasonably to have appreciated from emerging symptoms. Repeated near-misses, confusion, or visible disorientation may suffice to put a reasonable person on notice. Absent such indicators, sudden collapse may excuse breach. Courts will scrutinize the factual timeline closely.

Worked Example 1.3

Chloe, a long-distance driver with well-controlled type 1 diabetes, begins to feel light-headed and shaky. She eats a snack but soon experiences pronounced confusion and struggles to concentrate. Despite these symptoms, she decides to push on to the next service station 10 miles away. After drifting across lanes, she clips another car. Will Chloe be judged to have breached her duty?

Answer:
Likely yes. Once Chloe experienced noticeable signs of impaired functioning, a reasonable driver aware of such symptoms would have stopped immediately (or safely left the road) to test blood glucose and recover, rather than continuing. The scenario sits on the Roberts/Mansfield divide: unlike a sudden incapacitation without warning, the progressive symptoms were sufficient to alert a reasonable person to the need to stop.

Exam Warning

Be careful to distinguish between a defendant being suddenly incapacitated without warning (Mansfield) and a defendant who continues an activity despite realising they are becoming unfit (Roberts). Awareness of the impairing condition is essential in determining the applicable standard and whether it has been breached. Constructive awareness (what a reasonable person would have realized) is sufficient; the defendant cannot rely on subjective denial of symptoms.

Mental Illness and Disability

The application of the standard of care to defendants with mental illness or disabilities presents challenges. The law generally maintains an objective standard, reluctant to excuse defendants based on mental conditions unless the condition entirely eliminates fault.

The Objective Standard Maintained

Case law suggests that mental disability typically does not lower the standard of care expected. In Dunnage v Randall [2015] EWCA Civ 673, the Court of Appeal held that a defendant suffering from delusions due to schizophrenia, who unintentionally injured his nephew while setting himself on fire, was still required to meet the standard of care of a reasonable person. The court stated that only defendants whose medical condition entirely eliminates responsibility (e.g., rendering actions wholly involuntary) might be excused; otherwise, the objective standard applies. Mental illness is not in itself a defence to negligence where actions remain voluntary; the focus is on whether the defendant did, in fact, fall below the objective standard.

The policy rationale is clear: protecting claimants and ensuring compensation for harm where defendants’ acts were voluntary. The law avoids complex gradations of mental capacity at the breach stage and instead draws a firm line: unless the defendant’s acts were truly involuntary, they are judged objectively like any other person.

Key Term: Automatism (civil context)
A state in which actions are wholly involuntary, such that the defendant has no control over their bodily movements or conduct. In tort, only true automatism (entire loss of voluntary control) may justify excusing breach; impaired judgment or delusional beliefs are not enough.

True involuntariness is rare. Cognitive delusions or irrational impulses do not amount to automatism; courts require evidence that the defendant had no control over their movements or acts. If the defendant retains the ability to choose whether to act (even if that choice is influenced by mental illness), breach is assessed by the objective standard.

Worked Example 1.4

Nathan suffers an episode of psychosis. Believing he is surrounded by toxic gas, he runs from his house carrying a lit blowtorch to “burn off” fumes, accidentally igniting a neighbour’s fence. Nathan argues he was mentally ill and should not be judged by the reasonable person standard. Is that argument likely to succeed?

Answer:
No. Consistent with Dunnage v Randall [2015] EWCA Civ 673, mental illness does not lower the objective standard unless actions were wholly involuntary. Nathan’s decision to run with a lit blowtorch remains a voluntary act, even if irrationally motivated, so breach is assessed against the reasonable person standard.

Revision Tip

Remember that while physical conditions unknown to the defendant might prevent a breach (Mansfield), mental conditions generally do not lower the objective standard of care unless they negate voluntary action altogether (Dunnage). Evidence must show true loss of control (automatism), not just impaired judgment or delusional beliefs.

Children

The objective standard of care is modified for child defendants. A child is expected to show the level of care reasonably expected of an ordinary child of the same age.

Key Term: Child Standard of Care
The standard of care expected of a child defendant, judged by the conduct reasonably expected of a child of the same age, intelligence, and experience.

In Mullin v Richards [1998] 1 WLR 1304, two 15-year-old schoolgirls were fencing with plastic rulers. One ruler shattered, blinding the claimant in one eye. The Court of Appeal held the defendant was not negligent, as an ordinary, reasonable 15-year-old would not have foreseen the risk of injury. This contrasts with the standard expected of an adult.

The approach recognizes that children are less mature and risk-aware than adults. However, age is not a blanket excuse: the court asks what risk a child of that age would reasonably have appreciated and what precautions they could reasonably be expected to take. Context matters—organized play in a school corridor differs from engaging in obviously dangerous activities.

Worked Example 1.5

A 12-year-old, Amir, rides a kick scooter down a gentle slope in a park and collides with a pedestrian walking on the shared path. The pedestrian alleges negligence. How will the court assess breach?

Answer:
The court will apply the standard of a reasonably careful 12-year-old. If riding at moderate speed on a shared path was within what a reasonable child of that age would do, and the collision resulted from an unfortunate misjudgment rather than reckless conduct, breach is unlikely. If Amir had been weaving at high speed around pedestrians, a court might find that no reasonable 12-year-old would do so, and breach could be established.

Summary

Key Point Checklist

This article has covered the following key knowledge points:

• The standard of care in negligence is generally objective, based on the 'reasonable person'.
• Physical illness may affect the standard of care, particularly concerning the defendant's awareness of the condition and its potential impact.
• A defendant unaware of a suddenly incapacitating condition may not be in breach (Mansfield v Weetabix).
• A defendant aware of an impairing condition who continues an activity may be in breach (Roberts v Ramsbottom).
• Mental illness generally does not lower the objective standard of care unless it entirely negates fault (Dunnage v Randall).
• The standard of care for children is adjusted to that of a reasonable child of the same age (Mullin v Richards).
• Only true involuntary automatism can excuse breach; impaired judgment or delusions do not (objective standard maintained).
• Courts assess awareness objectively: what a reasonable person would have realized from the symptoms, not the defendant’s subjective view.

Key Terms and Concepts

• Standard of Care
• Reasonable Person
• Child Standard of Care
• Automatism (civil context)