“10. In many instances, an order for the costs of and caused by (or, as we used to say, occasioned by) an amendment or (asPD 17 puts it) the costs of and arising from the amendment, will meet the justice of the case. There will, however, be cases where the amendment abandons a particular cause of action that the defendant has spent a significant sum defending. Even in such cases, sometimes the amended statement of case will still pursue other causes of action arising out of the same facts, or the amendment will essentially just put a new label on previously pleaded facts such that the earlier costs have not been entirely wasted ... 11 Yet in other cases, the cause of action is simply abandoned, and substantial costs will have been wasted. An award of costs on the conventional basis would, in such cases, cover the defendant's costs of amending his defence to delete the now redundant answer to the abandoned plea, but would not recompense such defendant for the costs of investigating the original case or of pleading the first defence. On such facts, the usual order would not be just and the appropriate order will often be to award the defendant not just the costs of and caused by the amendment, but also the costs in respect of the abandoned cause of action.”