An International Guide to
Patent Case Management for Judges

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9.6.8 Evidence Evidence of fact

The typical issues of fact in a patents case are:

  • whether an item of prior art was made available to the public before the priority date, particularly if the prior art involves a prior use of something rather than a publication; and
  • the precise details of how the alleged infringing article or process operates.

In many cases, these questions will have been resolved before trial by the processes of disclosure and by admissions. If the matters are in issue, then evidence will be needed.

Evidence of fact can be admitted in patents proceedings by way of witness statements accompanied by any relevant documents as exhibits. The provision of trial witness statements is governed by Practice Direction 57AC of the CPR. Where a witness statement is being relied upon at trial, the evidence should be within the direct knowledge of the witness, who must be willing to be cross-examined on the contents of that witness statement or anything else about the case about which they have knowledge. The witness will be required to sign their witness statement with a clear statement that its contents are true. They will then be asked to reaffirm this under oath if they are called to give evidence at trial. Their written witness statement will generally stand as their evidence in chief at trial, so they will not be required to repeat it orally. As such, a witness’ oral evidence will be limited to cross-examination by the opposing party’s legal representative(s) followed by, if necessary, reexamination. Expert evidence

The provision of expert evidence in civil proceedings is governed by Part 35 of the CPR, supplemented by the Guidance for the Instruction of Experts in Civil Claims.128 As noted above, the court’s permission is always required to adduce expert evidence. Expert evidence is restricted to that which is reasonably required to resolve the proceedings.129

Patents cases are cases in which technical expert evidence is nearly always a critical part. In most cases, the parties will each call an expert or experts in the relevant discipline or disciplines. An expert’s duty is to help the court on matters within their expertise, and their role is to assist the court by providing objective, unbiased opinions on such matters.130 This typically involves the expert putting themselves into the shoes of the skilled person in the relevant art at the relevant date of the patent. An expert must be independent, and their duty to the court overrides any obligation to the party instructing them, despite the fact that that party may be responsible for their remuneration.131

To protect the expert witnesses – particularly from criticisms of lack of objectivity in approaching a piece of prior art with hindsight (i.e., with the invention in mind) – lawyers instructing experts typically provide instructions to the experts in a fairly regimented manner, following guidance from the courts.132 Expert reports are thus prepared carefully and in a sequential way so that the expert comments first on the common general knowledge and the prior art before they have sight of the patent in issue.

Expert evidence is provided in detailed written expert reports. An expert report must comply with the requirements set out in the Practice Direction 35 of the CPR at paragraphs 3.1–3.3. This includes the expert confirming in writing that they understand their duty to the court and have complied with it and that the expert is aware of CPR Part 35, its corresponding practice direction and the Guidance for the Instruction of Experts in Civil Claims.133

As with evidence of fact, an expert’s written report stands as their evidence in chief at trial, and they do not need to repeat it orally. At trial, the experts will nearly always be cross-examined at length by the opposing party’s legal representative(s) on the contents of their report and, if necessary, reexamined.

Besides technical evidence on the subject matter of the invention in the patent, expert evidence can also be provided, if needed, on other aspects of a case, such as the laws of other countries (by expert lawyers in the relevant jurisdiction).