Breach of duty

Once a duty of care is established, the claimant must prove breach: that the defendant fell below the standard of care required by law. Breach is a question of fact for the judge (or, rarely, the jury) and turns on an objective comparison between the defendant's conduct and that of the reasonable person in the defendant's position. The inquiry is not whether the defendant did their best, nor whether they behaved honestly or morally, but whether their conduct met the standard that the law demands.

The core test was articulated by Alderson B in Blyth v Birmingham Waterworks Co (1856) as the omission to do something which a reasonable man would do, or doing something which a prudent and reasonable man would not do. This simple formula conceals a rich structure of legal analysis: courts calibrate the standard by weighing the likelihood and gravity of harm against the burden of precautions, a calculus famously set out by Learned Hand J in United States v Carroll Towing Co and reflected in English law by Bolton v Stone and Watt v Hertfordshire County Council. Special rules govern breach by professionals (Bolam), children, and emergencies.

Proof of breach is governed by the ordinary civil standard (balance of probabilities). In some cases the maxim res ipsa loquitur may assist the claimant by permitting an inference of breach from the circumstances, though the modern tendency is to subsume this within general principles of inference rather than treating it as a rule of law.

This note traces the historical evolution of the breach standard, examines the risk-calculus framework and its application across varied contexts, analyses the special Bolam test for professionals, and explores doctrinal and academic controversies about objectivity, incremental duties, and the relationship between breach and duty.

The modern law of breach emerges from nineteenth-century attempts to rationalise liability in negligence. Before Donoghue v Stevenson [1932] AC 562 formalised the general duty of care, courts addressed breach within the confines of particular relationships. Alderson B's formulation in Blyth v Birmingham Waterworks Co (1856) 11 Ex 781 — the failure to do what the reasonable man guided upon those considerations which ordinarily regulate the conduct of human affairs would do — became the canonical statement and remains good law.

In Blyth, a water main laid by the defendants burst during an exceptionally severe frost, flooding the plaintiff's house. The court held that the defendants had not breached their duty: the frost was unprecedented and the defendants had taken precautions appropriate to ordinary winters. The judgment established two principles: the standard is objective (judged against the reasonable person, not the defendant's own abilities), and it is responsive to context (the reasonable person takes precautions proportionate to the foreseeable risk).

The probabilistic risk calculus was implicit in early cases but came into focus in the twentieth century. In Bolton v Stone [1951] AC 850, a cricket ball struck Miss Stone on the highway outside the ground. Balls had been hit out perhaps six times in thirty years. The House of Lords held no breach: the risk was so small that a reasonable person need not guard against it. Lord Reid observed that the standard is not perfection and must take account of the likelihood of harm. This foreshadowed the modern multi-factorial balancing test.

Paris v Stepney Borough Council [1951] AC 367 added gravity of harm to the equation. A one-eyed employee, injured when a metal chip struck his good eye, succeeded where a two-eyed employee might not have: the risk of total blindness made greater precautions reasonable. The House of Lords recognised that the standard varies with the potential severity of injury.

The mid-century cases thus refined Blyth into a nuanced calculus. By the 1970s, the House of Lords in Watt v Hertfordshire County Council [1954] 1 WLR 835 and later Tomlinson v Congleton DC [2003] UKHL 47 would articulate an explicit cost-benefit analysis that echoes Learned Hand's formula in United States v Carroll Towing Co 159 F 2d 169 (1947): breach occurs when the burden of precautions is less than the probability of harm multiplied by the gravity of injury (B < P × L).

The objective standard

The defendant is judged against the standard of the reasonable person (sometimes called the reasonable man or, latterly, the reasonable person of ordinary prudence). The inquiry is not subjective: the defendant's honest belief that they acted carefully is immaterial. In Nettleship v Weston [1971] 2 QB 691, a learner driver was held to the standard of the competent driver. Lord Denning MR stated that the law requires the same standard from all drivers, regardless of inexperience. The policy is one of loss distribution: the public expects a minimum standard and victims should not bear loss because the defendant is a beginner.

The standard is, however, objective with a built-in relativity. The reasonable person is notionally placed in the defendant's position, with the defendant's knowledge and sometimes (in limited contexts) the defendant's characteristics. A defendant with greater expertise is held to that higher standard (Wells v Cooper [1958] 2 QB 265). A child is judged as a reasonable child of that age (Mullin v Richards [1998] 1 WLR 1304), though not when performing an adult activity such as driving (Nettleship). Physical disability may also adjust the standard: a blind person is judged by what is reasonable for a blind person (Daly v Liverpool Corp [1939] 2 All ER 142, dicta), but mental illness or low intelligence does not reduce the standard (policy: difficulty of proof and need for victim compensation).

The risk calculus (Hand formula)

Breach involves a multi-factorial assessment of risk and precaution. The defendant breaches if a reasonable person would have taken precautions that the defendant omitted. The leading factors are:

1. Likelihood (probability) of harm: the more probable the injury, the greater the duty to guard against it (Bolton v Stone: very small risk, no breach; Haley v London Electricity Board [1965] AC 778: blind pedestrians are not so rare that reasonable precautions may ignore them).

1. Gravity (magnitude) of potential harm: the more serious the potential injury, the more precautions are required (Paris v Stepney). A risk of death or serious injury warrants greater care than a risk of trivial harm.

1. Burden (cost and practicability) of precautions: if a simple, cheap measure would eliminate the risk, failure to adopt it is more likely to be breach. Conversely, if precautions are prohibitively expensive or impractical, they may not be required (Latimer v AEC Ltd [1953] AC 643: factory flooded; sawdust spread to reduce slipping; closure not required because burden disproportionate to residual risk).

The case law on breach is cumulative rather than revolutionary. Each leading decision adds a factor or refinement to the objective standard and risk calculus.

Blyth v Birmingham Waterworks Co (1856) defines the standard itself and emphasises objectivity. It remains the doctrinal foundation: all subsequent elaboration flows from Alderson B's formulation.

Bolton v Stone [1951] AC 850 is the locus classicus for the probability factor. The House of Lords' refusal to impose liability for a very rare event (a cricket ball struck out of the ground perhaps once every five years) shows that reasonable care does not mean absolute safety. Lord Reid's speech is a model of proportionality reasoning.

Paris v Stepney Borough Council [1951] AC 367 demonstrates that the standard is sensitive to the claimant's particular vulnerability when known to the defendant. The one-eyed workman's case established that the gravity of the potential harm (here, total blindness) must be factored into the reasonableness calculus.

Latimer v AEC Ltd [1953] AC 643 illustrates the burden/practicability factor. The employer had spread sawdust after a flood made the factory floor slippery. The House of Lords held that closure of the entire factory was not required: the residual risk did not justify such an onerous precaution.

Watt v Hertfordshire County Council [1954] 1 WLR 835 addresses the social utility factor. Denning LJ's judgment recognises that emergency services may take greater risks when responding to save life. The case is often cited in examination questions involving ambulance drivers or fire brigades.

Nettleship v Weston [1971] 2 QB 691 confirms the objectivity of the standard: learner drivers are held to the same standard as experienced drivers. The Court of Appeal rejected a variable standard based on inexperience, citing insurance and victim protection. This remains controversial among academics who argue it conflates breach with policy-based strict liability.

Bolam v Friern Hospital Management Committee [1957] 1 WLR 582 and Bolitho v City and Hackney HA [1998] AC 232 together define the professional standard. Bolam defers to responsible professional opinion; Bolitho imposes a logical defensibility threshold. The tension between judicial deference and scrutiny of expert evidence has generated extensive academic commentary.

Montgomery v Lanarkshire Health Board [2015] UKSC 11 is the most significant recent decision. It limits Bolam and holds that in the informed consent context, the test is patient-focused (material risk disclosure) rather than profession-focused. Montgomery signals a broader shift towards patient autonomy and away from medical paternalism, with potential implications beyond consent (e.g., to advice and diagnosis, though this remains to be seen).

See practice questions below.

See further reading below.