Lessons in expert witness instruction from UK ruling in shower patent dispute

A recent UK Intellectual Property Enterprise Court (IPEC) judgment in a dispute between shower manufacturers Kohler Mira Limited (“Mira”) and Norcros Group (Holdings) Limited (“Triton”) highlights the importance of instructions given to expert witnesses in patent proceedings.

Expert witnesses are seen in virtually every patent dispute that reaches the UK courts. Courts in the UK tend to draw heavily on the opinions of expert witnesses and the role of experts is therefore often critical to the case outcome. Practitioners who regularly instruct expert witnesses will be aware of the various guidance on the use of expert witnesses in civil litigation proceedings in the UK, for example, Part 35 of the Civil Procedure Rules (“CPR”). 

The judgment in Mira v Norcros [2024] EWHC 3247 (Ch) provides a useful reminder of the importance of getting expert instructions right. 

Background

Mira is the owner of UK Patent No. GB 2,466,504 (the “Patent”) which was granted on 10 July 2013 and relates to an electric shower which has two or more outlets. 

There were two main types of shower on the market in the UK at the Priority Date (24 December 2008):

1. Mixer showers, supplied by hot and cold water feeds which are mixed to produce water of the desired temperature; and 
2. Electric showers, which are supplied by a cold water feed only, and contain one or more heating elements inside their casing to heat the water.

With electric showers, the slower the flow rate of water through the electric shower, the more time the water will spend in contact with the heating element(s) and the hotter the water will become. Therefore, if the flow from the electric shower is restricted entirely or to the extent that water flow is significantly impaired, the water may be heated to a temperature which is dangerous to the user. At the Priority Date, electric showers on the market were limited to those with only one outlet because of the risk of scalding if the water flow is significantly impaired during operation of a diverter valve to change the water outlet. 

Mira’s Patent covers a solution to this problem such that downstream of the heating element there is a diverter valve which is designed so that during changeover of the diverter valve, the outlet ports are never blocked to such an extent that water flow is significantly impeded. 

Mira claimed infringement of the Patent by Triton’s ‘DuElec’ range of electric showers which are marketed in the UK and have two outlets, such as an overhead shower and a hand shower.

Decision

The Court had to decide the following legal issues:

Validity

Was the Patent:

1. Novel over the key piece of prior art cited, UK Patent Application No. 2,274,985 A (“Deeley”)?
2. Obvious over (i) Deeley in conjunction with the common general knowledge, and (ii) the common general knowledge?
3. Insufficient?

Infringement

4. Did Triton’s DuElec showers infringe the Patent?

As regards validity, the Court found the Patent was novel over Deeley, not obvious, and sufficient, and therefore the Patent was held to be valid. As regards infringement, the Court found that Triton’s DuElec showers fell within the scope of claims 1 and 4 of the Patent, and so infringed it. 

Expert witnesses: key takeaways

The judge spends a significant portion of the judgment analysing the parties’ expert witnesses. It is also clear from the judgment that she preferred the evidence of Mira’s expert over that of Triton’s expert. The full reasons for this must be appreciated from the judgment itself, but here we summarise some of the criticisms made of Triton’s expert by counsel for Mira, much of which the judge agreed with, and draw out three key learnings.

1. Care should be taken when showing experts key documents

Deeley was the key piece of prior art cited by Triton in its validity attack on the Patent. Deeley describes a unit fed by separate hot and cold water feeds, and containing an electric pump and a diverter valve. It is therefore not an electric shower as it does not contain a heating element, but is a mixer shower with a pump to boost low pressure water supplies and two outlets which can be selected by the user. Within Deeley there is a cross-reference to UK Patent No. 2,219,497 B (“McMaster-Christie”). Deeley refers to an alternative invention being the incorporation of a water heater, as is described in McMaster-Christie, to the invention in Deeley.

The parties took different approaches to the provision of documents to…