Mental health, clinical negligence and the illegality defence

3 November 2020 by


In Ecila Henderson v. Dorset Healthcare University NHS Trust Foundation [2020] UKSC 43 the Supreme Court has revisited the defence of illegality (“ex turpi causa”) in the context of a claim for clinical negligence.

The claimant — a mental health patient — had committed a criminal offence as a result of the defendant health authority’s admitted negligence. Can a claimant, who would not have committed an offence but for the Defendant’s negligence, recover losses arising from their own criminality? Can they seek compensation for the pain, suffering and loss of earnings caused by a custodial sentence? Can they recover general damages for feelings of guilt and remorse? The Supreme Court answered these questions with a resounding “no”.

The Facts

Ms Henderson suffered from paranoid schizophrenia or schizoaffective disorder. Whilst under the care of the Defendant’s community mental health team she stabbed her mother to death. She did so whilst experiencing a serious psychotic episode. She was convicted of manslaughter by reason of diminished responsibility.

In sentencing her, the judge said that: “… there is no suggestion in your case that you should be seen as bearing a significant degree of responsibility for what you did”. The judge sentenced Ms Henderson to a hospital order under the Mental Health Act 1983.

Ms Henderson subsequently brought a civil claim against the Defendant Trust. The Trust admitted liability for its negligent failure to return her to hospital when her psychiatric condition deteriorated and accepted that, if it had done this, the tragic killing of Ms Henderson’s mother would not have taken place.

However, the Trust argued that Ms Henderson’s claim was barred for illegality (“ex turpi causa”), because the damages she claimed resulted from: (i) the sentence imposed on her by the criminal court; and/or (ii) her own criminal act of manslaughter.

The Supreme Court’s Decision

The central legal issue was whether the Court was bound by the House of Lords’ decision in Gray v. Thames Trains Ltd [2009] UKHL 33. A claim on very similar facts was dismissed in that case. Alternatively, the Court could depart from Gray in the light of the more recent decision of the Supreme Court in Patel v. Mirza [2016] UKSC 42. In that case the majority adopted a flexible policy based approach to the illegality defence which took into account competing public policy and proportionality factors.

The Supreme Court affirmed that the ex turpi defence was justified by two public policy considerations:

First, the need to ensure consistency between the criminal law and the law of tort. The integrity of the justice system depended on its consistency. It would inconsistent for the law, on the one hand, to imprison a person for the consequences of their criminality but, on the other, to compensate them for it. Or to put it another way the law should not “condone when facing right what it condemns when facing left”.

Second, the need to maintain public confidence in the legal system. It was offensive to public notions of the fair distribution of resources that a claimant should be compensated for the consequences their own criminal conduct. This would risk bringing the law into disrepute.

The Court held that conviction of manslaughter on the grounds of diminished responsibility meant that responsibility for the criminal act was diminished but not that it was removed. To allow recovery in civil proceeding would lead to inconsistency. It would attribute responsibility for the criminal act not, as determined by the criminal law, to the criminal but to the tortious defendant. The criminal under the criminal law would become the victim under the civil law. Moreover, to allow a civil judge to revisit the question of whether a convicted person bore personal responsibility for their crimes would create a clear risk of inconsistent decisions in the criminal and civil courts.

Applying the flexible policy based approach endorsed in Patel did not lead to a different conclusion. There was a strong public interest in the condemnation and punishment of unlawful killing.  Moreover the Court stated that:

NHS funding is an issue of significant public interest and importance and, if recovery is permitted, funds will be taken from the NHS budget to compensate the appellant for the consequences of her criminal conviction for unlawful killing.

The claimant relied upon countervailing policy considerations.  The policy of encouraging NHS bodies to care competently for the most vulnerable was one such policy. The policy of ensuring that public bodies paid compensation to those they had injured was another. The Court recognised that there was some force in these considerations. But they did not begin to outweigh those that supported the denial of the claim:

concern for the integrity of the legal system trumps the concern that the defendant be responsible.

Accordingly, Gray v. Thames Trains Ltd remained good law and was consistent with the policy driven approach in Patel v. Mirza.


This case provides helpful clarity for clinical negligence practitioners who bring or defend allegations of sub-standard mental health care. Following Henderson the general rule is that Claimants can recover for the personal consequences of self-harm as a result of negligent mental health care but not for the personal consequences of causing criminal harm to others.

This general prohibition applies to damages resulting from the imposition of a criminal sentence, such as general damages for the detention and loss of earnings during it. It also applies to damages for feelings of guilt and remorse  consequent upon a criminal act. Nor can claimants seek indemnities from defendants against claims brought by the victim or the victim’s dependents.

Interestingly the Court left open the possibility there may be some very exceptional cases where the defence of illegality would not apply. This may be where the criminal act committed as a result of the defendant’s negligence did not constitute ‘turpitude’. Examples might include trivial offences or strict liability cases where the claimant is not privy to the facts making his act unlawful (see [55-56] and [112]). The potential existence of this exceptional category follows from the application of the flexible policy based approach endorsed in Patel. In practice, the author would expect this exceptional category to apply very rarely indeed. However, it would not be a surprise if the limits of the illegality defence were tested in respect of a much less serious offence in the future.

Robert Kellar QC is a barrister at 1 Crown Office Row.

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