In a recent judgment by the Supreme Court of Appeal (SCA) in Strix Limited v Nu-World Industries (20453/2014)  ZASCA 126 (22 September 2015) 1 very important issue was dealt with succinctly by the court:
the court affirmed that a defence of lack of novelty is available even where the defendant does not use it in its counterclaim for revocation of a patent. Notwithstanding that, on the facts, the SCA held that lack of novelty defence failed.
It is now clear that the defence of lack novelty (and by extension, in my view, all extrinsic requirements of registrability of a patent including obviousness and inutility) need not form part of the initial counterclaim by the defendant in an infringement action/application.
Although most litigation attorneys/advocates would agree with the judgment, it does provide clarity on this issue.