If the defendant causes the victim to act in a foreseeable way, then any injury to the victim will have been caused by the defendant. This occurred in Roberts (1971)
R v ROBERTS (1971) - A girl jumped from a car in order to escape from sexual advances. The car was travelling at between 20 and 40 mph and the girl was injuered. The defendant was held liable for her injuries.
However, if the victim's acts are unreasonable, then this may break the chain of causation, as in Williams (1992).
R v WILLIAMS (1992) - A hitch-hiker jumped from Williams car and died from head injuries. The prosecution alleged that the driver had attempted to steal the victim's wallet. The court stated that the victim's act had to be foreseeable and also had to be in proportion to the threat. Here, the injury to the victim was not caused by the defendant