“One issue is: what is a suitably circumscribed issue? Or in other words, at what level of generality or granularity is that matter to be decided? Plainly it will vary from case to case. Often in patent cases one kind of suitably circumscribed issue and appropriate level of granularity is taking things at the level of individual cited items of prior art, but that is not a hard and fast rule. It is possible for a suitably circumscribed issue to arise within a broader category. An example of this was the Court of Appeal in ConvaTec Technologies Inc v Smith & Nephew plc[2015] EWCA 803 (Civ). Here, instead of dealing with the costs at the level of the issue of infringement as a whole, the court made a special order relating to experiments which formed part of the infringement case.”