AB v Chief Constable of X Constabulary

A claimant cannot recover damages for psychiatric injury where the injury was caused by his own voluntary criminal misconduct. The ex turpi causa principle applies even where the claimant was not prosecuted, provided the claim would award compensation for the consequences of that misconduct. In stress-at-work cases, ordinary employer’s liability principles apply. The claimant must establish reasonable foreseeability of the particular harm, breach of the reasonable steps required in the circumstances, and causation. It is insufficient to show merely that occupational stress caused the illness. The employer’s duty is not absolute and depends on the magnitude and gravity of the risk, the practicability and cost of preventative measures, and the justification for running the risk.

The claimant, a former undercover police officer, claimed damages for a chronic adjustment disorder and consequential financial loss. He alleged that the defendant, which accepted vicarious liability for the relevant police unit, had failed to provide adequate welfare support, supervision and monitoring during his deployment.

The defendant denied breach and causation. It contended that the psychiatric injury resulted from the claimant’s voluntary misuse of cocaine and the resulting loss of his undercover career. It also relied on the public-policy principle of ex turpi causa. The principal issues were causation, the application of that principle, and whether the alleged welfare arrangements fell below the standard required in a stress-at-work case.

1. Claim dismissed. Judgment was entered for the defendant.
2. The claimant’s chronic adjustment disorder was caused by the confrontation with his own misconduct and the sudden loss of his status and identity as an undercover officer. There was no accepted evidence of a psychiatric disorder before that event. Any breach concerning welfare, supervision or monitoring was therefore causally irrelevant.
3. The claim was also barred by ex turpi causa non oritur actio. Applying the wider rule identified in Gray v Thames Trains Ltd [2009] UKHL 33, the claimant could not recover damages for injury caused by his own voluntary criminal act, even though he had not been prosecuted. The public-policy approach described in Hounga v Allen [2014] UKSC 47 led to the same result. An award would compromise the integrity of the legal system, and there was no countervailing public policy requiring recovery.
4. In any event, breach was not established. The ordinary principles of employer’s liability applied, following the guidance reviewed in Sutherland v Hatton [2002] EWCA Civ 76. The relevant inquiry was whether the particular harm was reasonably foreseeable and whether reasonable steps had been taken in the circumstances. The measures identified for undercover officers were reasonable and had been properly implemented.
5. The court reaffirmed that the duty to prevent psychiatric injury from workplace stress is not absolute. The claimant must show that the breach caused or materially contributed to the illness, not merely that occupational stress caused it.