Application of the defence of “ex turpi”

In looking to the possible application of the defence of “ex turpi” in a claim of negligence arising out of a road traffic accident it could be crucial to ask whether the injury in issue was truly a consequence of the claimant’s unlawful act or whether it was a consequence of the unlawful act only in the sense that it would not have happened if the claimant had not been committing an unlawful act. In other words, could one say that, although the damage would not have happened but for the tortious conduct of the defendant, it was caused by the criminal act of the claimant; or was the position, rather, that, although the damage would not have happened without the criminal act of the claimant, it was caused by the tortious act of the defendant?