Mansfield v Weetabix [1998]

Court: Court of Appeal

Facts: The claimant, Tarleton, an employee of Weetabix, was driving a lorry while suffering from an undiagnosed medical condition that caused his blood sugar levels to drop, leading to hypoglycemia. This condition resulted in impaired driving and a series of accidents. Tarleton was initially found liable for the damages caused by the accidents. He appealed the decision, arguing that his medical condition should be taken into account when assessing his standard of care.

Issue: The key issue was whether the standard of care should be based on that of a reasonable person who is unaware of their impairment, or whether the reasonable person standard should apply to someone who has the condition, irrespective of their awareness of it.

Held: The Court of Appeal allowed the appeal, ruling that Tarleton should not be held to the standard of a reasonable person who is fully aware of their condition. Instead, the court found that the standard of care should be based on what a reasonably competent person, who is unaware of their impairment, would have done in similar circumstances.

Leggatt LJ, delivering the judgment, emphasized that the defendant's standard of care should be assessed according to their knowledge of their impairment. Since Tarleton did not know and could not reasonably have known about his condition, the standard of care was that of a reasonably competent person who was similarly unaware of their impairment.

Key Judicial Statement: Leggatt LJ stated, "The standard of care must be determined by reference to what a reasonable person would do if they were unaware of their condition. A person should not be held to a standard that requires them to mitigate an impairment they do not know they have."

💡 LevelUpLaw: Mansfield v Weetabix established that when a defendant is unaware of a mental or physical condition that affects their ability to act reasonably, the standard of care is based on what a reasonable person would do without knowledge of such a condition. This case recognized the need for flexibility in applying the standard of care in light of unknown impairments. However, it seems to be in apparent contradiction with Dunnage v Randall [2015], where the approach to mental illness in assessing the standard of care was different. Critics argue that Dunnage misunderstood the Mansfield key issue, which centered on the application of the standard of care in the context of unknown impairments.