Where an injury could have had more than one cause, what must be proved to establish causation? This issue has engaged the House of Lords on several occasions, and two differing answers have been forthcoming. The differing and inconsistent tests are categorised as the ‘material contribution’ test and the ‘but for’ or direct cause test.

The earliest authority on material contribution is Bonnington Castings Ltd v Wardlaw [1956] AC 613. In that case, a steel dresser had contracted pneumoconiosis as a result of exposure to silica dust emanating from both a pneumatic hammer and swing grinders. A statutory duty applied to the grinders, but not to the hammer. The issue was whether the dust that caused the injury came from the grinders or the hammer. It was held that, on the balance of probabilities, dust from the grinders had materially contributed to the injury, and on that basis causation had been established.

A similar approach was adopted in McGhee v National Coal Board [1973] 1 WLR 1. An employee contracted dermatitis having been required to empty brick kilns in dusty conditions. The medical evidence indicated that the cause had been repeated minor abrasions of the skin by particles of dust; the only way of avoiding the problem was the thorough washing of the skin after exposure to the dust. There were no adequate washing facilities at the workplace and the employee was unable to wash until he had returned home. While the medical evidence did not go so far as to establish that the employee would not have contracted dermatitis if he had been able to wash on site, it was held that the failure of the board to provide washing facilities on site had made a material contribution to the risk of injury. That was sufficient to prove causation.

In Fairchild v Glenhaven Funeral Services & Ors [2003] 1 AC 32, employees had developed mesothelioma from exposure to asbestos dust while at work, but there was uncertainty as to which of several employers was responsible for the exposure which had caused the disease. The Court of Appeal had held that for this reason causation could not be proved. However, the Lords held that, where there had been exposure by different employers but the precise causative point could not be identified, it was sufficient to find that the wrongdoing of each employer had materially increased the risk of contracting the disease.

Even so, in three other cases the Lords has favoured the ‘but for’ test.

In Hotson v East Berkshire Area Health Authority [1987] 1 AC 750, the plaintiff sustained a fall and was taken to hospital. Five days passed before his injury was correctly diagnosed and treated; he subsequently developed necrosis. Negligence had been admitted but causation remained an issue. There was a conflict of expert evidence. The Lords held that the weight of the evidence indicated that the injury was the primary cause of the necrosis. This was a ‘but for’ case and the evidence had not established that the delay was a causative factor.

Similarly, in Wilsher v Essex Area Health Authority [1988] 1 AC 1074 a premature baby required additional oxygen administered through a catheter. Unfortunately, the catheter was inserted in the wrong place but this was not noticed by the medical staff. The meters showed abnormal readings over a period of weeks and the baby developed fibroplasia which eventually resulted in blindness. The medical evidence was that there were four other possible causes of the fibroplasia apart from the excess oxygen administered. It was held that this was a ‘but for’ case and that no presumption could be made that the negligent insertion of the catheter made a material contribution to the injury.

In Gregg v Scott [2005] 2 AC 176, a lump under the claimant’s arm was diagnosed as benign, but it was a non-hodgkin’s lymphoma. By the time of the correct diagnosis some nine weeks later, the tumour had spread into the claimant’s chest. Treatment was only of limited success and the prospect of the claimant surviving for 10 years was assessed at only 25%. A majority of the lords held that the ‘but for’ test could not be satisfied because the claimant could not prove that the delay in diagnosis was the cause of his likely premature death.

The question has since been revisited by the Court of Appeal in Bailey v Ministry of Defence & Anor [2008] EWCA Civ 883. The claimant had been admitted to a hospital controlled by the ministry for an exploratory procedure relating to gallstones. After the procedure, there was defective care and resuscitation over a period of three days. Subsequently, she was moved to the intensive care unit at another hospital, by which time she had contracted severe pancreatitis. Her condition continued to deteriorate and after 17 days from her first admission, she had become so weak that she aspirated her vomit, resulting in a cardiac arrest and eventual brain damage. To an extent, the ministry admitted lack of care and failure to resuscitate. The remaining issue was whether the weakness could be causally linked to the lack of care and resuscitation or whether it would have been caused by the pancreatitis in any event. Counsel for the ministry submitted on the basis of Wilsher that the ministry’s failures did not satisfy the ‘but for’ test, the evidence having failed to establish any causal link between the failures and the weakness. In giving the judgment of the appeal court, Lord Justice Waller reviewed the two lines of authorities. He rationalised the position by holding that the ‘but for’ test was the appropriate test in a case where there were different and distinct factors that could have caused the injury, but where it was not possible to establish which had actually done so. However, following Bonnington Castings and on the evidence in the present case, any factor that could be shown to be a contributory factor to a more than negligible extent could and should be treated as a material contribution to the injury. Both the defective care and resuscitation and the presence of the pancreatitis were material contributions to the claimant’s weakness. No distinction should be drawn between medical negligence cases and other cases.

Bailey has subsequently been followed in Dickins v O2 Plc [2008] EWCA Civ 1144.

District Judge Tromans sits at Plymouth Combined Court Centre