Even in torts that are actionable per se, the claimant must prove that the tort caused the loss of which he complains if he wants to obtain substantial rather than nominal damages. Causation is concerned with the physical connection between the defendant's negligence and the claimant's damage. No matter how gross the defendant's negligence, he will not be liable if, as a question of fact, the conduct was not the cause of damage. The 'but for' test serves to exclude from consideration factors which have made no difference to the final outcome of events.
Sometimes the conduct satisfies the 'but for' test, yet it is merely one of a number of events that could be rightly regarded as causing harm. Clearly, the facts must have a bearing on the decision (factual causation), but in the final analysis the court has to make a choice as to which events are to be regarded as having sufficient causative potency. This is not a scientific enquiry but a process of attributing responsibility, and this involves value judgments and policy decisions.
It may be wrong however, to hold one responsible for all consequences of negligence. Sometimes, the outcome is freak or unusual and as such, it may not entirely be fair to put blame and accountability solely on the tortfeasor. Hence, the remoteness of damage that is the degree to which consequence of negligence and the type of consequence is anticipated from negligent conduct must be taken into account. Causation and remoteness are separate issues but they do tend to merge in practice. Lord Denning:
'The truth, all these terms – duty, causation and remoteness – are all devices by which the courts limit the range of liability… ultimately it is a question of policy for judges to decide' in Lamb v Camden London Borough Council . Causation – Claimant focus The 'but for' test – removing irrelevant causes If harm to the claimant would not have occurred 'but for' the defendant's negligence than that negligence is the cause of the harm. It is not necessary however, to be the cause because there may well be other events which are causally relevant.
Thus, if a loss would have occurred anyway then the defendant's conduct is not a loss Barnett v Chelsea and Kensington Hospital Management Committee  This is the authority for the 'but for' test. Here, the claimant was the wife of the deceased who died from arsenic poisoning. Upon feeling uncomfortable, he got medical attention but was negligently handled. Although negligence of the hospital was admitted, it was held that even if the hospital was not negligent, he would have still died.
Accordingly, the hospital was absolved of liability. Robinson v Post Office  It was held that the allergic reaction to the claimant would not have been discovered even if it was not negligently administered. As such, the doctor was not liable since it could not be established that 'but for' the doctor's negligence, the plaintiff would not have suffered. McWilliams v Sir William Arrol & Co. Ltd  This is the authority for breach of statutory duty that does not amount to liability.
The HoL held that it was probable that the deceased worker who was not given safety belt and subsequently fell to his death would not have worn it anyway from the overwhelming evidence gathered that they absolved the defendant. Bux v Slough Metals Ltd  – Limiting 'but for' Employers were held liable for failing to instruct and supervise employee in use of safety equipment. But safety equipment was provided. Sidaway v Bethlem Royal Hospital Governors  This is authority for medical risk disclosure.
Here, the patient alleges that his doctor had been negligent in disclosing risk information for a proposed procedure. However, even if such negligence is proven, he still had to prove that had the information been disclosed he would have declined the treatment, thus avoiding that risk. Thus, the defendants may be absolved of liability if the claimant cannot prove that 'but for' the defendant's failure to disclose relevant information she would not have undergone the treatment. The degree of disclosure is that described in the Bolam test. Chester v Afshar 
Court of Appeal held that in order to establish causation, the patient had only to prove that, had she been informed of the risks, she would have declined the particular procedure on the particular occasion on which the risk materialized, not that she would have refused ever to undergo the procedure – the claimant's damage consisted not in being exposed to the inherent risks of the procedure, which were always the same, but in causing the claimant to have an operation which she would not otherwise have had 'then and there'. JEB Fasteners Ltd v Marks Bloom & Co. 
This is the authority for negligent statements and advice. The claimant must establish not only that he placed real and substantial reliance on the defendant's advice though not only by itself a decisive part, in inducing the plaintiff to act to his detriment. Thus, he must establish that if he had not been given bad advice / statement, he would not have taken the course of action that he did. Sidaway, Chester and JEB is all to be subjectively analyzed. i. e. the question is of what this claimant would have done not what a reasonable claimant in that position would have done.