Whether the issue is seen as one of 'novus actus' or of contributory negligence (...) will depend upon the nature and quality of the plaintiff's conduct, and it may be that a positive act is more likely to break the causal chain than a mere omission (cf. Knightley v. Johns (CA, 1982) (...)). On any view of the matter McKew v. Johns seems to be a harsh decision. There may be instances where even a deliberate act by the plaintiff will not relieve the defendant of responsibility.