Professional Negligence – Clearing the Causation Hurdle

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It is all well and good identifying potentially negligent acts and then instructing an expert to provide you with a report that a professional has acted negligently. But this alone is not enough to pursue a successful claim before the courts. Having established negligence, the next step before finally calculating loss is demonstrating causation. But what does this involve?

Causation is the link between the negligence act and loss. In order to successfully clear the causation hurdle the party making the claim most prove that had it not been for the negligent act, they would have not suffered the loss claimed. If the negligent act made no difference to the claimant’s course of conduct or how matters eventually would have panned out, then the case will fail on grounds of causation.

Causation is often overlooked or misunderstood, especially at the early stages of claims

Factual Causation - The “But for” Test

The above analysis is referred to as the “but for” test. “But for” the defender's negligence, the loss would not have occurred. The test was developed in the case of Barnett v Chelsea & Kensington Hospital Management Committee. It is a somewhat dramatic example.

Three men attended the emergency department of the hospital run by the Management Committee. The duty doctor did not see them and sent them home to contact their GPs. One of the men died some hours later. The post mortem showed arsenic poisoning was the cause of death.

It was decided, that on the “but for” test, even if the deceased had been examined and admitted for treatment, there was little or no chance that he would have survived. Although the hospital had been negligent by sending him home, the causation hurdle had not been cleared. The upshot of this is that even in cases of clear-cut (or even admitted) negligence, success is not a forgone conclusion.

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Legal Causation

Whilst the Barnett case was about the factual cause of the loss, there is also the doctrine of legal causation. This is a trickier concept. Causation in law can be established by showing that the defendant's act was the operative and substantial cause of the loss and that there was no intervening event i.e. that it was the main cause of the loss complained of.


When considering a claim of professional negligence issues of causation can be equally important as the negligent act itself. The difficulty is often that until a report has been obtained spelling out exactly what went wrong, a claimant is not in a position to turn the clock back and apply the “but for” test. Despite this issues of causation should be carefully considered before embarking on any court proceedings or expensive investigatory process.

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