It's the primary school teacher's well-rehearsed refrain. It's also (almost) the facts of Johnson v Silverlink Trains Limited, heard in Coventry County Court on 23rd February 2011.
Mrs Johnson was on her way back from seeing Robbie Williams, along with about 65,000 others. She rushed to Milton Keynes station where a throng of people was blocking the entrance. Mrs Johnson's case was that a station guard directed her under a cordon bearing the message 'Police- Do Not Cross'. As Mrs Johnson ducked under the cordon, she lost her balance and fell flat on her face, sustaining unpleasant injuries.
The facts were in dispute and the judge actually found that Mrs Johnson had not been specifically directed to duck under the cordon.
But even if she had been, the judge accepted the Defendant's argument that liability did not follow. Mrs Johnson was an adult, the risk of losing her balance going under the cordon was obvious, and at most the guard had permitted her, not obliged her to go under it. She freely and voluntarily decided to go under the cordon and that was the cause of the accident. Even if there was a breach of duty, there was a break in the chain of causation.
What are the principles that determine whether a claimant’s actions are a ‘novus actus’ that breaks the chain of causation?
Voluntary or Deliberate Act
A key point is whether the claimant is properly in control of his actions or not. So where a claimant responds with a panic or reflex reaction to an emergency brought about by the defendant, he is not properly in control of himself precisely because of the emergency the defendant has caused. In such a case the claimant’s actions are unlikely to break the chain of causation.
Corr v IBC Vehicles Ltd  2 WLR 299 was in this category. There, the claimant’s husband had committed suicide after suffering depression and post-traumatic stress disorder following an accident at work for which the defendant accepted liability. The question was whether the suicide broke the chain of causation. On the facts, the House of Lords held that the suicide, though a deliberate, conscious act, was a direct result of depressive illness, which impaired the deceased making reasoned and informed judgments about his future. The House of Lords contrasted this to a Canadian case where the court found that the deceased had made a conscious decision to end her own life, there being no evidence of disabling mental illness leading to incapacity in her facility of volition.
So, unsurprisingly, when the court found that the claimant in Wilson v Coulson  PIQR P22 QBD was, despite suffering brain damage in a road accident, still able to take a voluntary, deliberate and informed decision to take heroin, the defendant was not liable for the consequences of this.
The more unreasonable the claimant’s conduct is, the more likely it is to break the chain of causation. This comes from the House of Lords’ decision in McKew v Holland and Hannen and Cubitts (Scotland) Ltd  3 All ER 1621. The claimant in that case had injured his leg which was left liable to give way at any moment. He descended steep stairs with no handrail. The leg gave way and with no handrail or adult support he fell, sustaining serious injuries. The House of Lords considered the claimant had acted unreasonably: the weakness in his leg meant he should be careful. He was not and this failure broke the chain of causation.
In rescue cases the rescuer’s conduct is very unlikely to be considered unreasonable, even when the claimant puts his own life or limb at risk. This is because “the cry for distress is a summons for relief”.
Similar considerations apply where the claimant is dealing with an emergency. In Sayers v Harlow UDC (1958) 1 WLR 623 the claimant found herself locked in a public lavatory. She shouted and banged the door but no-one came to help. She tried to escape by climbing out and in so-doing placed her foot onto the toilet roll – which, as it was designed to do, rotated, causing her to fall. The defendant argued this was wholly unreasonable and won at first instance. The Court of Appeal disagreed: given the situation the claimant found herself by reason of the defendant’s default, trying to escape was reasonable and the accidental placing of her foot on the toilet roll was a misjudgment rather than something so unreasonable as to be a novus actus.
Some caution is needed using “unreasonableness” as the touchstone. In the more recent case of Spencer v Wincanton Holdings  PIQR P8 on similar facts to McKew but where the claimant succeeded Sedley LJ doubted “unreasonableness” was helpful, preferring to consider a formulation based on “fairness”.
Value Judgment / Fairness
Following on from Spencer, in Corr the House of Lords brought these threads together in terms of fairness. This requires a value judgment of the claimant’s actions looking at the facts in the round. So where an act is a voluntary, informed decision it may well break the chain of causation. Where an act is unreasonable, it may break the chain of causation. But an unreasonable act that is not truly voluntary or informed (such as suicide where the balance of the deceased’s mind has been disturbed by the defendant’s tort) will not.
It’s important not to forget the exception to the rule too. In the particular case of police guarding a person in custody who had been identified as a suicide risk, the police are under a duty to ‘protect the person from himself’ as set out by the House of Lords’ decision in Reeves v Commissioner of Police for the Metropolis (2000) 1 AC 330. This exception comes about because of the particular and specific nature of the duty in question and as such is likely to be confined to custody cases.