## Facts

- Ms. Henderson suffered from paranoid schizophrenia and was under the care of Dorset Healthcare University NHS Trust.
- In 2010, during a psychotic episode, she fatally stabbed her mother and was convicted of manslaughter by reason of diminished responsibility.
- Ms. Henderson brought a negligence claim against the Trust, asserting that its failure to provide adequate care contributed to her mental state at the time of the killing.
- The Trust admitted negligence but argued that the claim was barred by the illegality defence (ex turpi causa non oritur actio).
- Both the High Court and the Court of Appeal held that the illegality defence barred her claim.
- Ms. Henderson appealed to the Supreme Court, specifically regarding the applicability of the defence in the context of her mental disorder.

## Issues

1. Whether the claimant, whose loss arose from her own criminal act of manslaughter committed under a mental disorder, could recover damages for negligence against the healthcare provider.
2. Whether the illegality defence should apply when the claimant’s unlawful conduct was influenced by a mental disorder.
3. Whether public policy considerations permit a claim when the criminal act is directly linked to the loss, despite mitigating mental health factors.

## Decision

- The Supreme Court unanimously dismissed Ms. Henderson’s appeal.
- It held that the illegality defence barred her claim for losses arising directly from her own criminal act, even where the act was influenced by her mental disorder.
- The Court emphasized that the defence applies where the unlawful conduct is an essential part of the claim.
- The Court stated that mental health factors that may mitigate criminal responsibility do not negate the operation of the defence in civil claims.
- The judgment reaffirmed that the illegality defence acts as a rule of law, not on a discretionary basis.

## Legal Principles

- The maxim ex turpi causa non oritur actio prevents claimants from recovering damages for losses resulting from their own criminal conduct.
- The illegality defence is rooted in public policy, maintaining the integrity of the legal system by precluding benefit from unlawful acts.
- The defence applies where the loss for which damages are sought is directly linked to the claimant’s criminal act, regardless of mental disorder influencing the act.
- Mental illness may mitigate criminal responsibility but does not automatically preclude application of the defence in tort.
- The ruling clarifies that public policy priorities may outweigh mitigating personal circumstances in determining civil liability.

## Conclusion

The Supreme Court in Henderson v Dorset Healthcare University NHS Trust [2020] UKSC 43 reaffirmed that the illegality defence bars recovery for losses arising from a claimant’s own criminal conduct, even where that conduct was influenced by mental illness. The decision prioritizes the integrity of the legal system and public policy considerations over individual mitigating circumstances, providing clarity for future negligence claims involving both criminal acts and complex mental health issues.
