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Patents: Cross-Examination of Expert Witness

Medico Legal

Audrey Horton – Bird & Bird LLP The Court of Appeal has considered the effect of the decision not to cross-examine the patent owner’s expert witness on his opinion on obviousness


Generally, a party is required to challenge incross-examination the evidence of any witness of theopposing party if he wishes to submit to the court thatthe evidence should not be accepted on that point.This rule gives the witness the opportunity ofexplaining any contradiction or alleged problem withhis evidence.

If a party has decided not to cross-examine on aparticular important point, he will have difficultysubmitting that the evidence should be rejected.However, the rule is not an inflexible one. Failure toput a relevant matter to a witness may be mostappropriately remedied by the court permitting therecall of that witness to have the matter put to him(Phipson on Evidence. 19th Edition, 2016).


B sued E for infringement of two patents for artificialheart valves.

The High Court held that one patent was valid andinfringed, but that the other patent was invalid forobviousness.

B and E both called two expert witnesses: aninterventional cardiologist, a clinician who might implant a replacement heart valve; and a bio-medicalengineer, who might design one. There were threerounds of exchange of expert reports before the trial,although B’s rejoinder report was made only by theirbio-medical engineering expert.

E did not cross-examine B’s cardiologist expert onthe prior art. Both parties appealed.


The court dismissed the appeals. It held thatalthough the rule on cross-examination set out inPhipson was important, it was not inflexible.

Where it was proposed to save time by not cross-examining two witnesses in relation to the same orsimilar subject matter, it was good practice for thematter to be raised with the court beforehand, so thatit could give directions in the light of the parties’submissions. Directions should ensure fairness to the without incurring unnecessary costs byextending the length of the trial. However, the factthat such a direction was not sought or given did notautomatically require the court to accept an unchallenged reason given by one expert.

The rule requiring important positive evidence to bechallenged was, generally, a rule not simply for thebenefit of the witness whose honesty or professionalreliability was challenged, but was also designed toensure the overall fairness of the proceedings for theparties. The rule applied with particular force wherea witness gave direct evidence of a fact of which hehad knowledge and which it was proposed to invitethe court to disbelieve. Fairness to the witness and tothe parties demanded that the witness should be challenged on his factual evidence so as to give him theopportunity of affirming or commenting on the challenge, or on a positive matter which it was proposedto set against his evidence.

Not every situation however called for a rigidapplication of the rule. At least part of the unfairnesswhich the rule was intended to address was the lackof any opportunity for a witness to respond to achallenge to his evidence. Here B put in three roundsof expert evidence, so each expert had more thanample opportunity to comment on the views of theother. The potential for unfairness to the witness inthese circumstances was much reduced.

In particular, B’s expert evidence could not beregarded as unchallenged, because, by the time hewent into the witness box, B’s expert had seen andhad the ability to comment on the contrary technicalopinion of E’s expert and had seen the same challenges put to B’s other expert. This was a wholly different situation to one where a witness had no noticeof the nature of the challenge to his evidence and nofair opportunity to comment on it.

Although B’s experts had different expertise, theywere both given evidence on how a collaborativeskilled team would have undertaken a hypotheticaldesign project, and were qualified to do so. Consistently with that, B’s expert had expressed himself in his first report in terms which showed he consideredhe was able to speak on behalf of the whole team. So,there was a genuine overlap between the evidence ofthe two experts and both were making exactly thesame technical points. The court was justified inthinking that B would not be able to identify anypoint which was exclusively for the clinician as eachexpert had claimed the ability to make the samepoints. Even if the overlap had been raised by E, thecourt should not have required both experts to becross-examined on these points as this would haveincreased the length of the trial unnecessarily.


This decision shows how general rules of procedureand evidence may not always apply in the specialisedcircumstances of patent litigation. Here, as in mostpatent cases, there had been several exchanges ofexpert evidence. Those advising the parties may havegood reason for deciding to limit cross-examinationof their opponent’s expert witnesses. In these cases, itis advisable to raise the decision in advance so thatboth parties can raise concerns and the court can givedirections in light of the submissions. Failure to seekdirections re not cross-examining two witnesses onthe same subject-matter did not mean the unchallenged evidence of one expert witness must beaccepted. Here, acceptance of the evidence of anexpert witness who was not individually challengedin cross-examination did not render the judgmentunsafe.

Case: Edwards Lifesciences LLC & Ors v BostonScientific Scimed Inc (2018) EWCA Civ 673.

First published in the May 2018 issue of PLC Magazine and reproduced with the kind permission ofthe publishers. Subscription enquiries 020 7202 1200

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