Illegality, insanity and negligence claims after Lewis‑Ranwell [2026] UKSC 2

In the recent judgement Lewis-Ranwell v G4S Health Services (UKSC/2024/0040), the Supreme Court held that the illegality defence can bar a negligence claim even where the claimant was found not guilty by reason of insanity for unlawful killings that sit at the centre of the loss claimed. The court treated the case as a “novel situation” (para 120), rejected a “bright line” approach that would make illegality turn on criminal responsibility, and applied the structured policy analysis in Patel v Mirza to conclude that allowing the claim would undermine the coherence and integrity of the legal system.

The appeal was allowed, with the consequence that the pleaded negligence heads of loss (including claims for detention-related loss and an indemnity against victims’ claims) are barred by illegality on the assumed facts underpinning the strike‑out/summary judgment applications.

Facts and procedural history

In February 2019, Alexander Lewis-Ranwell killed three men during a severe psychotic episode, having been arrested twice shortly beforehand and released on bail. The Supreme Court stressed that it was deciding the appeal in the context of strike‑out/summary judgment applications, meaning it had to work on assumed facts: “it is necessary to proceed on the assumption that the claimant will make good at trial all the allegations in his pleaded case” (para 2).

The defendants (and appellants) included G4S Health Services (UK) Limited, Devon Partnership NHS Trust and Devon County Council. The alleged negligence concerned failures in mental health assessment and care while the claimant was in custody and in contact with services. The claimant’s pleaded causation case was that, but for those failures, he would have been admitted to hospital before the killings and would not have committed them or suffered the later consequences (including detention under mental health legislation).

At the criminal trial, the claimant was found not guilty of murder by reason of insanity. He then brought civil claims, including a negligence claim seeking wide‑ranging heads of loss and an indemnity against civil claims by victims’ families.

The appellants applied to strike out the negligence claim (or obtain summary judgment) on illegality grounds. The High Court refused to strike out. The Court of Appeal, by a majority, dismissed the appellants’ appeals, largely treating criminal responsibility (and knowledge of wrongfulness) as a critical dividing line. The Supreme Court allowed the appeal.

Legal framework

The case sits in the modern “policy‑based” illegality doctrine, shaped by Patel v Mirza. The Supreme Court reiterated that illegality is a public policy doctrine, not a merits-balancing exercise between the parties.

For present purposes, two aspects of the court’s legal framing are especially important.

First, unlawfulness is not limited to criminal conviction. The court said, at the threshold stage, that “there is no difficulty in saying that the conduct of the claimant was unlawful so as to engage the illegality defence” (para 121). It also made clear that the absence of criminal offences (because of the insanity verdict) “should not be a decisive consideration” (para 122).

Secondly, the court treated Patel as providing the structured template. In direct terms: “Patel has provided a structured analytical template for the assessment of whether to uphold the defence of illegality” (para 44). That template, as the judgment applies it, asks (in summary) whether denying the claim enhances the purpose of the prohibition transgressed, whether doing so harms other relevant public policies, and whether denial is proportionate in the particular case.

The court also noted the “adaptive flexibility” of remedies: in appropriate cases, illegality may exclude some heads of loss but not others. That observation mattered because, in this case, the Supreme Court concluded the claimant’s unlawful conduct was central to the loss pleaded.

Court’s reasoning and holdings

A “novel” illegality question, but an incremental answer

The court squarely acknowledged that it was dealing with a gap in direct domestic authority: “we are confronted by a novel situation on which there is no direct authority in this jurisdiction” (para 120). It therefore proceeded “step‑by‑step”, applying established principle and developing it incrementally.

That “novelty” was not the idea of illegality in homicide-related clinical negligence claims (those already existed in earlier cases), but the specific configuration: unlawful killings, followed by a not guilty by reason of insanity verdict, followed by a negligence claim seeking damages for consequences of those acts (including detention and an indemnity).

Rejecting the “bright line” between diminished responsibility and insanity

A key submission (accepted by the Court of Appeal majority) was that illegality should only bite where the claimant was criminally responsible and knew their conduct was morally or legally wrong. The Supreme Court rejected that as too narrow and too dependent on moral culpability. It addressed the Court of Appeal’s approach head‑on:

“While the application of that distinction to the illegality defence may not be irrational, we respectfully disagree that it is appropriate.” (para 125)

The court’s criticism was not that culpability is irrelevant, but that it is not the organising principle. It said the Court of Appeal placed “too much weight on the absence of moral culpability” and failed to focus on coherence and the integrity of the legal system, which the Supreme Court treated as central to illegality analysis.

The judgment also reframed the insanity/diminished responsibility divide as a difference on a spectrum of mental illness severity, rather than a switch that should control civil illegality policy. The court put it succinctly: “That difference is not critical to the applicability of the policy considerations required under Patel” (para 127).

The insanity verdict still establishes “unlawful” conduct for illegality purposes

A practical anxiety for civil practitioners is whether an insanity verdict means the claimant has not committed an “illegal” act in the relevant sense. The Supreme Court’s answer was clear. It noted that, although there was “no finding of criminal responsibility”, the verdict established the claimant did the acts: “The jury’s verdict, however, established that he did the acts – he killed the three men – but was insane” (para 128).

That matters because the court treated the killings as unlawful for illegality purposes. The analysis is grounded in coherence: the civil law’s response should not allow recovery that cuts across how other parts of the legal system respond to unlawful killing and the protective detention it triggers.

Applying Patel: coherence, public confidence, and proportionality

The heart of the judgment is the Patel balancing exercise. The Supreme Court framed the central concern in terms of internal legal consistency:

“The court is entitled and required to take a broad view of the underlying policies including those relating to the internal consistency of the law and the integrity of the legal system.” (para 144)

On the assumed facts, the court identified multiple forms of incoherence that would follow if a civil court awarded damages flowing from lawful detention ordered after the killings, and from liabilities arising out of the killings themselves.

On remedies, the judgment tied particular heads of loss to established illegality logic. It said the attempt to recover compensation for detention ordered by the criminal court “falls within Lord Hoffmann’s narrower rule in Gray” (para 146). The indemnity claim was treated as especially problematic: “In bringing the claim for an indemnity the claimant is seeking to rely on his own wrongful acts” (para 149).

The court did not dismiss competing public interest considerations. It accepted that it is “in general in the public interest that the courts should adjudicate civil wrongs”, and it acknowledged that civil claims might expose failures and raise standards. But it pointed to “alternative procedures, such as inquests and public inquiries” as better suited to scrutinising systemic failings.

At proportionality stage, the court’s focus was bluntly on the gravity and centrality of the conduct to the claims pursued. It highlighted: “The brutal killing of three innocent men is of the utmost seriousness” (para 162(1)), and concluded: “denial of the claim would not be a disproportionate response to the illegality” (para 163).

Outcome

The Supreme Court held that, despite the absence of criminal responsibility, the illegality defence is engaged and applies on the pleaded case, and it allowed the appeal: “For these reasons we would allow the appeal” (para 172).

The judgment also recorded two limits to what was before it: there was no strike‑out application by the police defendant, and the other defendants did not pursue strike‑out of the Human Rights Act claims, which appeared likely to proceed.

Practical implications for practitioners

This is a case about early case analysis and pleading discipline. It speaks to claimant and defendant solicitors in clinical negligence, public authority negligence, and tort claims where the claimant’s own unlawful act sits at the centre of the alleged loss.

For claimant advisers, the judgment is a warning that an insanity verdict is not, by itself, a route around illegality where the claim seeks to shift consequences of unlawful killing onto others. The court treated the underpinning concern as system coherence and public confidence, and it found the claimant’s conduct “central to all heads of loss claimed” (para 162(2)). Claims drafted around detention-related loss, reputational loss, lost earnings caused by detention, and indemnities against victims’ claims should be treated as high‑risk in illegality terms.

For defendant advisers (including NHS bodies and outsourced providers), the judgment strengthens the utility of early applications where the pleadings reveal that the claimant’s unlawful conduct is the effective cause of the losses. The Supreme Court treated illegality as a “substantive defence” rather than “a procedural bar on access to a court” (para 155). That framing supports a strategic decision to seek strike‑out or summary judgment where the pleaded losses fall squarely within the kind of incoherence the court identified.

For both sides, the court’s recognition that illegality can be tailored by head of loss remains important. It suggests that careful pleading and careful analysis of causation chains may still matter in other cases where some losses are genuinely separable from the unlawful act. However, whether and how far a claimant can plead and prove separable heads in a fact pattern like this is not fully worked through in the judgment and is therefore unspecified beyond the court’s finding on these pleadings.

Finally, the judgment’s nod to inquests and public inquiries is a practical steer for those acting for families, public bodies, and care providers: where the objective is scrutiny of systemic failings rather than damages, the court signalled that other mechanisms may be better suited. It also specifically noted an inquest into the deaths had been opened.

Six takeaways for solicitors:

• Test illegality early: In triage, ask whether the pleaded loss flows from the claimant’s unlawful conduct; if yes, consider Patel analysis upfront.
• Do not treat insanity as a safe harbour: An insanity verdict may remove criminal responsibility, but the act can still be “unlawful” for illegality purposes.
• Scrutinise detention-related heads of loss: Claims for compensation for lawful detention after unlawful killing are especially vulnerable.
• Treat indemnity claims as a red flag: Indemnities against victims’ claims are likely to be attacked as reliance on the claimant’s own wrongful acts.
• Use tailored remedies where possible: Where losses are separable, consider whether illegality should bar only some heads; separability on the facts may be disputed or unspecified.
• Consider parallel processes: If the aim is accountability and learning lessons, inquest/public inquiry routes may be more effective than damages litigation.

Concluding reflections

This judgment extends the direction of travel from earlier homicide‑linked illegality cases into the specific territory of insanity. The Supreme Court’s core message is that the illegality defence is driven by coherence and integrity, not by a binary distinction based on criminal responsibility or moral culpability. Where the pleaded losses are the consequences of unlawful killing, and especially where the claim seeks compensation for detention imposed to protect the public or an indemnity for liabilities to victims, the court’s view is that allowing recovery would undermine the legal system’s coherence.

Unspecified details include the claimant’s and defendants’ wider evidential positions on duty, breach and causation (beyond the assumed facts for strike‑out), the eventual fate of any Human Rights Act claims (not pursued on illegality in this appeal), and client‑specific context such as sector focus and publication deadline.

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