A man with longstanding mental health issues walks into a pub with a can of petrol and a knife. He proceeds to pour the petrol on himself and says he is going to burn the pub down. The police are called, he is arrested and whilst in police custody, he undergoes a Mental Health Act assessment.

It is alleged that the assessors negligently fail to recommend transfer to a secure psychiatric unit. The man alleges that he suffered an exacerbation of his mental health as a result of being transferred to a medium secure prison where he witnessed various unpleasant acts that he would not have witnessed in a secure psychiatric unit.

These were the facts in a claim I recently dealt with. The man (the Claimant) brought a claim for damages for personal injury for the exacerbation of his mental health. The Defendant made an application to strike out the claim on the basis that it was barred by the illegality principle.

This case seemed to me a good time to take stock of where the law stands on the principle of illegality. When it arises, it is often in clinical negligence cases.

The Law

The most recent decision on the illegality principle was in the Supreme Court decision of Henderson v Dorset Healthcare University NHS Foundation Trust [2021] AC 563.

In Henderson, the Claimant stabbed and killed her mother whilst experiencing a psychotic episode. Her plea of manslaughter by reason of diminished responsibility was accepted by the Crown and she was sentenced to a hospital order. The Defendant NHS trust admitted negligence in failing to return the Claimant to hospital by reason of her manifest psychotic state and admitted that but for this failure, the Claimant would not have killed her mother. However, the Defendant denied liability on the basis that the damages claimed were a consequence of the sentence imposed by the criminal court and/or her criminal act of manslaughter.

The Supreme Court accepted the Defendant’s argument. In doing so, it approved the categorisation of wide and narrow public principles from the earlier case of Gray v Thames Trains Ltd [2009] AC 1339.

In Gray, the Claimant was a passenger on a train involved in the Ladbroke Grove train crash. He suffered PTSD and later stabbed and killed a pedestrian who stepped in front of his car. Like in Henderson, he pleaded guilty to manslaughter by reason of diminished responsibility and was sentenced to a hospital order.

In Henderson, Lord Hamblen summarised the claim in Gray as follows:

“The claim for damages included damages which were the result of the sentence imposed on him, such as general damages for his detention and loss of earnings during it (‘the narrow claim’). It also included damages which were the result of the killing, such as general damages for feelings of guilt and remorse consequent upon the killing and an indemnity against any claims which might be brought by dependants of the deceased (‘the wide claim’).”

In Henderson, the Supreme Court approved Gray and it remains good law.

Applying the Law to the Facts

In my claim above, it was conceded that the Claimant could not recover damages for the fact of being detained. Instead, the Claimant’s argument was that he was challenging the manner, rather than the fact, of his detention. He argued that the Mental Health Act assessment was an intervening act and he was owed a duty of care to be managed properly within the prison system, in the same way as a prisoner who fell in unsafe prison premises might bring a claim under the Occupiers’ Liability Act 1957.

At first instance, the judge accepted this argument, holding that it was an intervening act which was under challenge and the claim was not caught by the illegality principle.

On appeal, that decision was overturned and it was held that the claim was caught by the illegality principle. What was relevant was that the Claimant, having later pleaded guilty to various offences, was remanded by the Magistrates Court and was sentenced by the Crown Court. Both of those were decisions of the criminal courts which could not be challenged in a civil claim. Those decisions not only dealt with the principle of detention but the manner of it. Therefore, the Claimant could not get around the difficulty that his claim involved asking the civil courts to make a finding inconsistent with that of the criminal courts.

The Future

The cases show that the courts have held firm on the illegality principle. In every case, Gray included, Claimants have sought to distinguish it and to argue that because of a particular set of facts, it does not apply. The courts have consistently held that it does.

For future cases, it can fairly be said that any further arguments by Claimants as to why the principle does not apply is likely to be met with short shrift. The appetite is simply not there for a dilution or reformulation of the rule. As Lord Hoffmann said in Gray:

As one commentator has said ‘Tort law has enough on its plate without having to play the criminal law’s conscience’: see EK Banakas [1985] CLJ 195, 197”.