BUILDING DISPUTE – dispute between owners corporation and builder – where defendant builder seeks to commence separate proceedings against the developer to rectify the contract pursuant to which the building was constructed – related application to amend list response in present proceedings to incorporate that defence – where it has been open to the defendant to agitate the question of rectification for three years – where substantial effort and expense has gone into the preparation of the case as currently pleaded – where a variation argument is in any event already provided for – consequence that it is not in the interests of justice to allow defendant the leave it seeks.