In McKew v Holland & Hannen & Cubitts (Scotland) Ltd. (1969) 3 AER 1621, the defendant's negligence caused an injury to the claimant's leg that significantly weakened it.
If he had given the matter a moment's thought, he would have realised that he could only safely descend if he went extremely slowly and carefully so that he could sit down if his leg gave way.
In Wieland v Cyril Lord Carpets (1969) 3 AER 1006 the defendant's negligence caused an injury to the claimant's neck that necessitated the wearing of a surgical collar.
The claimant also wore bifocals and the collar inhibited the normal compensatory movement of her head to maintain perfect vision.
Eveleigh J. said that "...one injury may affect a person's ability to cope with the vicissitudes of life" but all that arises reasonably in the ordinary course of events will not break the chain.
In Sayers v Harlow UDC (1958) 1 WLR 623 having paid to use a public toilet, a 36-year-old woman found herself trapped inside a cubicle that had no door handle.
The court held that the injuries she suffered were a natural and probable consequence of the defendant's negligence, but that the damages would be reduced by 25% since the claimant had been careless in depending for support on the toilet-roll holder.
The current thinking would not support limiting damages by a figure of 25% and if, for example, the claimant was thrown out of the vehicle because no seat belt was worn, a substantial finding of contributory negligence should follow.
Indeed, in Hitchens v Berkshire County Council the High Court expressed some difficulty in following the logic of Lord Denning's figure of 25% although the ratio decidendi was considered binding.
There are two further principles to consider: If a claimant is volens, they have willingly accepted the risk of being injured by the foreseeable behaviour of the defendant.
In Morris v Murray (1990) 3 AER 801 the claimant helped an obviously drunken pilot get into a small aeroplane, which crashed as it attempted to take off.
The court held that the claimant must have known the condition of the pilot and voluntarily took the risk of negligence by agreeing to be a passenger.
Similarly, under ss1 and 2 Unfair Contract Terms Act 1977, commercial agreements seeking to exclude liability in negligence are also void.
The problem is that if the medical evidence of the head injury establishes that the criminal conduct would not have arisen "but for" the tort alleged then, in principle, damages should follow.