The Supreme Court unanimously dismissed the appeal in Henderson v Dorset Healthcare University NHS Foundation Trust on 30 October 2020. James Goudkamp was a member of the Counsel team instructed by the respondent.
Henderson is a landmark decision concerning the illegality defence. It confirms that the policy-based approach to the defence endorsed in Patel v Mirza  UKSC 42;  AC 467 applies not only to claims for unjust enrichment (that being the type of claim in issue in Patel) but across private law. It also provides significant guidance on how the Patel test is to be applied.
The facts of Henderson were tragic. The claimant killed her mother while suffering from paranoid schizophrenia. She was convicted of manslaughter by reason of diminished responsibility and was sentenced to detention in hospital. The claimant then sued the NHS in negligence. She alleged a failure to provide her with proper care and contended that had reasonable care been taken she would not have killed her mother and would not, in turn, have incurred any liability under the criminal law. The claim was resisted on the basis of the illegality defence.
The Supreme Court held that the defence applied. Delivering the reasons of the Court, Lord Hamblen, following Patel, held that the balance of relevant policy factors supported denying the claim and that denying the claim would not be disproportionate. Numerous points of significance emerge from the judgment including the following.
- Lord Hamblen confirmed that the approach to the illegality defence propounded in Patel is not limited to the unjust enrichment setting. His Lordship remarked that “there can be little doubt that [Patel] was intended to provide guidance as to the proper approach to the common law illegality defence across the civil law more generally” (at ).
- However, Patel does not represent “year zero” on the law governing the illegality defence. Rather, earlier authorities remain relevant to the extent that they are compatible with the policy-based approach to the defence enunciated in Patel (at ).
- The decision of the House of Lords in Gray v Thames Trains Ltd  UKHL 33;  1 AC 1339, which laid down a causation-based approach to the illegality defence, is Patel compliant (at ). That is because that causation-based approach is suffused with policy considerations, and emphasises the importance of consistency between tort law and the criminal law.
- Although reliance by the claimant on his or her own wrongdoing was rejected in Patel as the overarching test for the illegality doctrine, that does not mean that the issue of reliance is not a relevant factor (at ).
- Certain policy factors will, when relevant, tend to have significant weight attached to them including the policy that the law should not facilitate wrongful profiting and that the law should be coherent (at ).
- The policy-based test espoused in Patel does not necessarily require that the issue of proportionality be considered. Rather, if the balance of policy factors points against denial of the claim, it is unnecessary to address the issue of proportionality. Lord Hamblen described Patel as adopting a “disproportionality check rather than a proportionality requirement” (at ).
- Where it is necessary to enquire as to proportionality, the centrality of the offending and the closeness of its causal connection with the claim will often be important considerations (at ).
Although Henderson is not a commercial case, Lord Hamblen’s guidance given regarding the policy-based test endorsed in Patel evidently applies to commercial cases that raise the illegality defence.
James Goudkamp was instructed by DAC Beachcroft LLP (Bristol). He has published extensively regarding the illegality defence and tort law more generally. His publications include his award-winning book Tort Law Defences and the leading tort textbook Winfield & Jolowicz on Tort.
Please view the judgment here.