The most important factors to bear in mind with a registered design infringement case are as follows
i) Assess the registered design;
ii) Assess the accused object;
iii) Asses the prior art.
Quite simply the most important factor is what the design looks like. By and large it should be possible to decide a registered design case in a few hours. The evidence of the designer, e.g. as to whether he/she was trying to make, or thought he/she had made, a breakthrough, is irrelevant. The evidence of experts, particularly about consumer products, is unlikely to be of much assistance: anyone can point out similarities and differences, though an educated eye can sometimes help a bit. Sometimes there may be a piece of technical evidence which is relevant – e.g. that design freedom is limited by certain constraints. But even so, that is usually more or less self-evident and certainly unlikely to be controversial to the point of a need for cross-examination still less substantial cross-examination.
Most registered designs are for consumer articles, objects bought or to be appreciated by ordinary members of the public.
Experts are not usually required in cases involving registered designs for consumer products. There is a feeling amongst lawyers that one must always have an expert, but this is not so. No-one should feel that their case might be disadvantaged by not having an expert in an area when expert evidence is unnecessary. Evidence of technical or factual matters, as opposed to consumer ‘eye appeal’ may, on the other hand, sometimes have a part to play–that would be to give the court information or understanding which it could not provide itself.
The spirit and effect of the CPR require the court to look even more closely at the need for expert evidence. In registered design actions, I think the court should take care before allowing any expert evidence. In particular, the court should know precisely to what areas that expert evidence will be directed. If blanket permission is given, each side feels compelled to get an expert who then has to say something. What is then said has to be read by the other side. Thereby time and cost to no particular use is expended.
It is for instance, clear law that whether or not the defendant copied is irrelevant; see, for example, per Aldous J. in Gaskell & Chambers Ltd v. Measure Master Ltd  R.P.C. 76, 81. So it is irrelevant for the claimants’ witness to throw down a challenge that he thought the defendant copied, as was done here, and it is equally irrelevant for the defendant to prove or to give disclosure about how his design was arrived at.
Similarly, it is irrelevant for the claimant to prove, if it be the case, that he spent a fortune in arriving at his design. It matters not whether he thought of it in the bath or by engaging the most prestigious design consultants in the world. One area of evidence which I think is admissible, and is of some secondary assistance, is the reaction of the public and trade (who expect to sell to the public) to the design.