Duty to Warn CASES

In English law, there is no general duty to warn. Instead, a duty to warn may arise in specific contexts as part of the obligation to take
reasonable care. Whether a warning is required depends on the relationship between the parties, the nature of the risk, and what a
reasonable person would do in the circumstances.

Definition and principles

A duty to warn concerns the need to inform another person of risks, dangers, or limitations that are not obvious and that may cause harm if
not disclosed. It is not a standalone duty, but a way in which a defendant may discharge their duty of care and avoid breaching the required standard.

The adequacy of a warning depends on its content, clarity, and timing. A warning must be sufficient to enable the recipient to make an
informed decision or take reasonable steps to avoid harm. In some cases, providing a warning may not be enough if the risk remains
unreasonably high.

Common contexts

Duties to warn commonly arise in medical negligence, where patients must be informed of material risks of treatment; in product liability,
where manufacturers warn of dangers associated with use; and in occupiers’ liability, where visitors must be alerted to non-obvious hazards. Professionals giving advice may also be required to warn clients of significant risks or limitations.

Key cases

• Montgomery v Lanarkshire Health Board: established the modern standard for warning patients of material risks.
• Latimer v AEC Ltd: illustrated that warnings may be relevant but are not always sufficient.
• Vacwell Engineering Co Ltd v BDH Chemicals Ltd: recognised a duty to warn of known dangers in supplying products.

Legal implications

Failure to give an adequate warning may amount to a breach of duty, leading to liability where harm results. Conversely, an appropriate and
effective warning may reduce or eliminate liability by demonstrating that reasonable care was taken.

Practical importance

The duty to warn plays a significant role in managing risk and allocating responsibility across a wide range of activities. It emphasises
the importance of informed choice, transparency, and communication in professional and commercial relationships.

See also: Negligence; Breach of duty; Medical negligence; Occupiers’ liability; Product liability; Professional negligence.