P was infected with hepatitis after a blood transfusion from a donor with the disease. At the time the risk of such infection through blood transfusions, though known to the medical profession, was impossible to avoid, either because the virus itself had not yet been discovered or because there was no way of testing for its presence in blood. P brought a claim against D under the Consumer Protection Act 1987 and D argued that the “knowledge” defence applied. It was accepted by D that liability for a defective product (in this case blood) was regardless of fault. The court held that the directive’s purpose was to make liability strict (to make claims easier) and therefore lack of “avoidability” of damage was not one of the circumstances to be taken into account and nor was the impracticality, cost or difficulty of precautionary measures, and the benefit to society or the utility of the product relevant. The question was ascertaining legitimate expectations. Here the blood was defective because there were no warnings and it was legitimate to expect that the blood would be free from disease. The defence based on “knowledge” in s.4 did not apply where the existence of the generic defect was known or should have been known in the context of accessible information. Once the existence of the defect was known, there was the risk of that defect materialising in any particular product, and it was immaterial that the known risk was unavoidable in the particular product, since it would defy the point of the directive if a producer let dangerous products go to market simply because he didn’t know which of his products were dangerous.