One of the key differences between the UK patent litigation system and the continental system is the role of expert evidence, in particular when it comes to inventive step. German courts consider obviousness to be a question of law, the role of the experts being only to shed light on the knowledge and mindset of the the person skilled in the art at the priority date. Finding a compromise between both of these positions will surely be a crucial task to tackle in the first decisions of the UPC.
In the decision American Science & Engineering Inc v Rapiscan Systems Ltd  EWHC 756 (Pat) (11 April 2016) , justice Arnold shares the following general comments on how to instruct the expert:
General comments on the expert evidence
109. Each party contends that the other party instructed its expert to ask himself the wrong question. Both sides' solicitors proceeded in a carefully structured manner by first asking their expert to consider the person skilled in the art and the common general knowledge, then to consider the prior art relied upon by Rapiscan and only then to consider the Patent. The difference between them was that AS&E's solicitors asked Dr Bjorkholm to consider obvious developments of the prior art before showing him the Patent, whereas Rapiscan's solicitors only asked Dr Lanza to consider the question of obviousness after they had shown him the Patent.
110. In my view there is force in the criticisms which each side levels at the other's approach. The approach adopted by AS&E's solicitors had the advantage that it enabled Dr Bjorkholm to consider obvious developments of the prior art free from knowledge of the Patent; but it meant that he never addressed in his reports the question of whether the differences between Swift and the claimed invention constituted steps which would have been obvious to the person skilled in the art. The mere fact that a step did not occur to Dr Bjorkholm when reviewing the prior art was not sufficient to exclude the possibility that he might agree that it was obvious if asked. Unlike the person skilled in art, real people sometimes miss the obvious.
111. The approach adopted by Rapiscan's solicitors avoided that difficulty. The problem is that, whereas the correct question is whether, viewed without any knowledge of the claimed invention, the differences constituted steps which would be obvious, Dr Lanza expressed his understanding of the question he had been asked to consider without referring to the need to exclude knowledge of the claimed invention. Moreover, this does not appear to have been an artefact of the drafting of the report. On the contrary, Dr Lanza confirmed in cross-examination that his approach had been to consider obviousness as if the skilled person had been shown the claims and asked if they were obvious. Thus Dr Lanza does not appear to have understood the importance of trying to avoid hindsight.