Patent Litigation in Practice Series: Spotlight on the UK: The use of experts

Every month our international team of patent litigation experts provide a practical insight into different aspects of patent litigation in their jurisdiction. We start with the UK and how experts are used.

“...incapable of scintilla of invention… also very forgetful… an assembly of nerds of different basic skills, all unimaginative” but “not a complete android” (Technip France SA’s Patent [2004] EWCA Civ 381).  

A template for a good online dating profile, this is not.  Instead, these are the essential characteristics of the notional skilled addressee of a patent in the UK. It is through the eyes of this skilled person (or skilled team) that the UK courts must approach many of the key facets of patentability, from claim construction through to obviousness.  

The UK courts are not unique in relying on expert evidence in order to help understand how the skilled person would have understood certain concepts at a relevant date. Yet it is perhaps the approach for how these experts are instructed and deployed that, to those on the outside, might seem strange.  Let us look into this in a bit more detail.

Role of an expert in the UK

The primary function of an expert is to educate the court in the technology of the patent. Throughout their role, the expert owes an overriding duty to the court and not to the party instructing them (see Civil Procedure Rules (‘CPR’), Part 35). Their evidence will usually take the form of a written report, plus one or more reports submitted in reply to the evidence of the opposing party.  An expert may (but not always) give further oral evidence by way of cross-examination during trial. This evidence must be independent, unbiased, uninfluenced by the pressures of litigation and the expert should not assume the role of an advocate (Practice Direction to CPR35).  

Preparation of the expert’s report

There is an onus on the instructing solicitors to help ensure that their expert is able to meet their duties under the CPR.  In recent years there has been a particular focus on how expert evidence is prepared in patent cases and the sequence in which experts are shown documents (Fisher & Paykel v Flexicare [2020] EWHC 3282 (Pat)). 

In short, judges’  preferred approach is:

  1. First ask the expert about the common general knowledge (‘CGK’) relating to their field; 
  2. Next,  show the expert the relevant prior art and to ask them questions such as what steps would be obvious to take in light of the document(s); and 
  3. Only then, to show the expert the patent-in-suit.  

This approach is often referred to as “sequential unmasking” (Akebia v Fibrogen [2020] EWHC 866 (Pat)).  The aim is to try to mitigate hindsight creeping into the expert’s analysis of what would be obvious (or non-obvious) to try.  If an expert has seen the patent before discussing the CGK or the prior art, their opponent  may argue that their view on, for example obviousness, always had a particular end-point in mind and, therefore, is no longer free from bias.  

Although a preferred approach, this is not an absolute requirement by the UK courts. There may be occasions where new prior art comes to light only once the patent has been discussed or the expert may already have seen prior art or even the patent before being instructed. None of these are absolute barriers for that expert continuing to work on the case. However, any pre-existing knowledge should be properly identified in the expert reports and care should be taken to ensure that the expert has remained independent (Advanced Cell Diagnostics v Molecular Instruments [2024] EWHC 898 (Pat)).  

The practical reality of this sequential unmasking approach can also lead to significant costs and timing pressures for the parties.  It may not be known until after the discussion of the patent what position an expert might take on critical issues. If this is so, the instructing solicitors may need to restart the process of discussing CGK and prior art with an alternative expert. 

Teams of experts

Under the rules  the evidence of an expert must be limited to their area of expertise.  In complex patents, this may mean that the notional skilled addressee of a patent is not an individual skilled person but a skilled team of experts.  Where real teams of experts would collaborate on a project, recent case law has emphasised the need for “corresponding teams of expert witnesses to consult one another in a broadly similar way” (Sandoz v Bayer [2024] EWHC 896 (Pat)).  It may also mean that, within the skilled team, there is one expert who would be considered a “leader” of the hypothetical skilled team. 

Scientific advisors

Alongside expert evidence the UK courts also have the power to appoint a scientific advisor (s.70(3) Senior Courts Act 1981 and CPR rule 35). The role of a scientific advisor is much more discrete and will generally be focused on providing a non-controversial scientific background for the court by way of a primer or teach-in.

Such scientific advisors are usually deployed during appeal proceedings (as the appellant courts will not have the benefit of hearing live expert evidence) as a supplement to any expert report and are not regularly used in first instance trials.  It is usual for the scientific advisor to assist only during the judge’s pre-reading and not during trial. Indeed, a recent decision from the Patents Court confirmed that a scientific advisor should not be used as a substitute to expert evidence where there are likely to be technical points of disagreement between the parties (Hill v Touchlight [2024] EWHC 533 (Pat)). 

Key takeaways

The role of experts remains a central tenet to patent proceedings in the UK. Key to this is the requirement that the experts remain independent and free from hindsight. 

Whilst not an absolute requirement, parties are well-advised to follow the preferred approach of sequential unmasking.  This may be particularly important to bear in mind where there are parallel proceedings in jurisdictions where experts can be shown the patent at a much earlier stage.  In these circumstances it may be advisable to engage separate experts for the UK proceedings. 

Written by Charlie Davies