Ps had been exposed to asbestos by different employers over different times and they caught a disease from it. However it could not be proved which specific exposure caused the disease or at which moment it was contracted, so that no tortfeasor could be said on the balance of probabilities to have caused the disease. HL held that in such a case (i.e. the specifics of this case where the source of the problem is undoubted but it is impossible to pinpoint a particular moment or D that caused the disease) there was no need to prove “balance of probabilities.” Instead all that was necessary was that each defendant's wrongdoing had “materially increased the risk” of contracting the disease. Within these guidelines, claims could be founded against all the employers.
Lord Bingham: this type of modification is necessary where the injury is caused by slow build up and not one sudden infliction. There are policy arguments either way for the principle of the “increase the material risk of harm”. Against it are: (1) an employer for only a short period of time might be punished; (2) an employer who didn’t cause the harm might be made liable. However FOR it are (1) the idea that P should be compensated for injury that his employer should have done more to prevent; (2) to exclude the rule would be to prevent all claims for injuries which are caused by a development over time rather than at one moment, as here.
Lord Nicholls: the doctrine is necessary in cases of two or more alternative causes to prevent patent unfairness: suppose A and B are hunting and shooting carelessly so that one of them (it is unknown which) shoots and injures passer-by C. If causation had to be proved beyond reasonable doubt then there would be no compensation. It is more unfair that a victim should not be compensated than that a hunter who didn’t cause the harm should be punished (since he is doing something inherently fault-worthy). Where good policy reasons exist, the court can depart from the “balance of probabilities” rule. However these reasons must be so good that it is worth depriving D of the protection afforded to him by the normal evidentiary rule. He also said that “considerable restraint is called for in any relaxation of the threshold ‘but for’ test of causal connection”, that “Policy questions will loom large” and that it was “impossible to be more specific”.
Lord Hoffman: There are 5 features that justify an exception to the general rule on “balance of proof”: “First, we are dealing with a duty specifically intended to protect employees against being unnecessarily exposed to the risk of (among other things) a particular disease. Secondly, the duty is one intended to create a civil right to compensation for injury relevantly connected with its breach. Thirdly, it is established that the greater the exposure to asbestos, the greater the risk of contracting that disease. Fourthly, except in the case in which there has been only one significant exposure to asbestos, medical science cannot prove whose asbestos is more likely than not to have produced the cell mutation which caused the disease. Fifthly, the employee has contracted the disease against which he should have been protected.”
Lord Rodger: conditions for an exception are: (1) impossibility of proving who caused the harm. (2) D materially increased probability of P being harmed. (3) D’s conduct must have been capable of causing P’s injury. (4) D has to prove that his injury was caused by one kind of event (e.g. exposure to asbestos: NOT exposure + unhealthy lifestyle + working in a mine etc). (5) That it was caused by agencies operating in the same way e.g. two types of dust ARE allowed.