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  What’s relevant?

It isn't always clear what expertise is required. What then happens when there is some ambiguity about the precise nature of ‘the relevant field of expertise’?

The Court looked again at the difficulties posed when there is some ambiguity about the precise nature of ‘the relevant field’ in the case of Environmental Defence Systems Ltd -v- Synergy Health plc.

In that case a challenge was made to the validity of a patent for barrage units used for flood defences. The method of the invention was to make water-absorbent pads and arrange them within a porous sack to form the barrage unit. The court was required to determine inventive step as a preliminary issue.

The difficulty in this case was that the method of manufacture of the pads was similar to that used in the manufacture of incontinence pads and nappies. The defendant asserted that it had been performing the totality of the claimed invention prior to the grant of the claimant’s patent. The defendant also claimed a right under the Patents Act 1977 s.64 to continue an act performed before the priority date, and asserted that the patent was invalid. The Court was required to determine whether there was an inventive step in using the method of manufacture of the absorbent pads in the manufacture of a barrage unit.

The Court directed that each party could call one expert witness, but the direction did not state the technical subject matter to be addressed by the experts. The claimant adduced evidence from an expert in personal hygiene products, while the defendant employed an expert in flood risk management.

The Court held that the starting point for identifying a person skilled in the art was Catnic Components Ltd -v- Hill & Smith Ltd, where it was stated that a person skilled in the art was likely to have a practical interest in the subject matter of the invention, and practical knowledge and experience of the kind of work in which the invention was intended to be used. On the face of it, this supported the claimant’s choice of expert. However, while the characteristics of the skilled person in relation to insufficiency would be those identified in Catnic, that might not be true of the skilled person through whose eyes inventive step was to be assessed.

The Court pronounced that a party seeking to invalidate a patent should state clearly in the pleading the technical field nominated for the skilled person so far as inventive step was concerned, including an explicit statement of the skilled person’s background. It was also necessary to state the argument on inventive step. In response, the patentee should set out the counter arguments concerning inventive step and address the common general knowledge of the skilled person drawn from the technical field selected by the defendant. By the time of a case management conference it should be clear how many experts are needed and in which disciplines. In this case, the parties had failed to address the field from which the skilled person should be drawn in respect of inventive step.

The Court, finding in favour of the defendant, held that it was likely that by the start of the relevant period the skilled person would have been aware that barrage units could be made by filling a bag with absorbent polymer. The skilled person was assumed to already know how to make absorbent pads, which would be an obvious choice as a filler. There was nothing to suggest that fibrous material would be regarded as undesirable as a filler in a barrage unit. Further, it would have appeared to the skilled person that the absorbent pads would be worth trying as fillers for a barrage unit, with a reasonable expectation of success. It followed that there was no inventive step in the patent, nor was there inventive step arranging the pads in the bag.

Making his judgment, Judge Hacon commented that it was his impression that both sides thought that details of the skilled person, including the technical field from which he came, were best left to be argued at trial. This, he said, was not something that should have been deferred until that relatively late stage. The practical consequence of the way the proceedings had progressed was that the defendant was not pinned down to a nominated skilled person until he served his expert evidence.


In the face of increasing limitations on the use of expert witnesses (and particularly the possibility that the parties will be reduced to relying on the evidence of one expert only), it is important to get this right. If it should transpire, at some point later in the proceedings, that the wrong expert might have been instructed, then it would be appropriate for a party to apply to the court to make an adjustment to the directions. While leave may or may not be granted, it would be preferable to simply leaving the point to be argued out at trial.


  • Environmental Defence Systems Ltd -v- Synergy Health plc [2014] EWHC 1306 (IPEC).
  • Catnic Components Ltd -v- Hill & Smith Ltd (No.1) [1981] FSR 60.



Issue 85
February 2015

Consequences of choosing the wrong expert
What’s relevant?
Paying LiP service to justice

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