# Breach of duty in negligence: the standard of care

> **Key takeaway:** Breach = fall below reasonable person / competent professional standard. Balance risk vs precautions. Professionals: Bolam + Bolitho; clinical consent risks: Montgomery. Seriousness and likelihood of harm both matter. Practice codes help but are not decisive.

- **Jurisdiction:** England & Wales
- **Practice area:** Commercial
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Commercial/breach-of-duty-negligence
- **Keywords:** breach of duty, standard of care, Bolam, Bolitho, Montgomery, reasonable person, professional negligence, negligence

## What is this about?

Once a duty of care is established, the claimant must show breach: that the defendant failed to meet the standard of care the law requires. The general standard is the reasonable person in the defendant's position, adjusted for professional skill, special risks, and (in limited ways) the defendant's characteristics. Breach is fact-sensitive and often turns on risk magnitude, practicability of precautions, and common practice.

## What is the core rule?

A defendant breaches a duty of care by falling below the standard of the reasonable person (or the reasonably competent professional in that field) in the circumstances. The court balances the likelihood and seriousness of harm against the cost and difficulty of precautions (and any social utility of the activity). Professional defendants are generally judged by responsible professional practice (Bolam), subject to the court's power to reject illogical practice (Bolitho) and to the Montgomery approach on informed consent in clinical advice cases.

## What are the elements or test?

1. Identify the applicable standard: ordinary reasonable person, learner/child adjustments where relevant, or skilled professional standard
2. Assess foreseeable risk: probability and gravity of injury (Paris v Stepney for seriousness; Wagon Mound (No 2) for small risks of grave harm)
3. Weigh practicable precautions and burden of taking them against the risk (including activity utility where relevant)
4. For professionals: was the conduct supported by a responsible body of opinion (Bolam), and is that opinion logically defensible (Bolitho)? For consent to treatment risks: Montgomery patient-focused disclosure
5. Use of common practice and codes: relevant but not conclusive

## Which authorities matter?

- **Blyth v Birmingham Waterworks Co (1856) 11 Ex 781** — Classic formulation of negligence as omitting to do something a reasonable person would do, or doing something a reasonable person would not.
- **Bolam v Friern Hospital Management Committee [1957] 1 WLR 582** — Professional standard: not negligent if acting in accordance with a practice accepted as proper by a responsible body of professionals in that art.
- **Bolitho v City and Hackney Health Authority [1998] AC 232** — Court may disregard professional opinion that is not capable of withstanding logical analysis.
- **Montgomery v Lanarkshire Health Board [2015] UKSC 11, [2015] AC 1430** — For material risks and treatment alternatives in clinical advice, the doctor's duty is to take reasonable care to ensure the patient is aware of material risks; not a pure Bolam question.

## How does this apply in practice?

This note covers the breach stage only. Duty, causation, remoteness, and defences are separate. Res ipsa loquitur may assist proof of breach in some unexplained-accident cases but does not reverse the legal burden in the modern sense without care. Statutory duties and health-and-safety regimes may supply concurrent or alternative routes.

## What are common pitfalls?

- Applying hindsight rather than the foresight of the reasonable person at the time
- Treating Bolam as conclusive in every clinical dispute after Montgomery (consent) and Bolitho (logic review)
- Equating breach with any adverse outcome — damage alone does not prove substandard care
- Ignoring magnitude of risk when the probability looks low but potential harm is severe

## When would a practitioner use this?

Use when advising on liability in personal injury, professional negligence, and occupiers' cases after duty is conceded or established.

## Quick reference

Breach = fall below reasonable person / competent professional standard. Balance risk vs precautions. Professionals: Bolam + Bolitho; clinical consent risks: Montgomery. Seriousness and likelihood of harm both matter. Practice codes help but are not decisive.

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*