In  Tehrani v Hamilton Bonaduz AG & Ors [2021] EWHC 3457 (IPEC) HHJ Hacon considered a case where a claimant appeared as their own expert witness.

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The claimant, a professor, brought an action asserting that the defendant infringed her patent in relation to the method of controlling a ventilator.   The claimant had legal representation, however she gave evidence, as an expert, on her own behalf.


The Witnesses
    1. There were two expert witnesses.  Prof. Tehrani gave expert evidence on her own behalf.  Since 1994 Prof. Tehrani has been Professor of Electrical Engineering at California State University, Fullerton, California.
    1. There is no necessary reason why an expert should not be closely connected to the party for which he or she is giving evidence, such as being an employee.  But in such instances there is an inevitable risk that the expert’s views could be coloured by loyalty to his or her employer.  There may be a higher than usual requirement for the expert to show, by the answers given and manner in which they are given, that their clear and primary duty while giving evidence has been to assist the court objectively and truthfully.  In this instance the expert was both claimant and inventor of the patent in suit.  That requirement was more acute.
    1. I am sorry to say that Professor Tehrani did not provide the necessary indication of her objectivity.  I think that she came to court to argue her case and that her evidence was given in that spirit.  I do not suggest that Professor Tehrani had the intention of misleading the court, but it was my strong impression that she could persuade herself of the truth of matters that fitted her view of the case.  It does not follow that she was wrong about such matters.  However, I was not always sure that what she said was fair and accurate.
    1. I give an example.  Professor Tehrani alleged that the work done by two teams who published papers, each of which was pleaded as an item of prior art, contained false research which had been forged.  Three of the four members of one of those teams were physicians at Harvard Medical School.  The other paper was written by an engineer from the Department of Electrical Engineering at the University of Wyoming and a physician at the Alaska Native Medical Center.  Irrespective of the relevance of these allegations, they were serious, inherently unlikely to be true and were not shown to be true.  Yet I do not doubt that Professor Tehrani believed her allegations to be accurate.
    1. I give a second example.  In her first witness statement Professor Tehrani set out propositions which, she said, were part of the common general knowledge of the skilled person at the priority date.  They were not supported by references to textbooks or anything else, they were just assertions.  When challenged about this in cross-examination, her answer was to dismiss the idea that she had to support anything that was so obviously accepted by everyone in the field.
    1. All too often during cross-examination a challenge to something Professor Tehrani had said was likewise dismissed as a challenge borne solely of ignorance.  Professor Tehrani did not give me confidence that her evidence was accurate and objective.
  1. Hamilton’s expert was Professor Stephen Rees.  He is Professor at the Respiratory and Critical Care Group, Department of Health Science and Technology, Aalborg University in Denmark.  Professor Rees’ carries out research in the development, validation and application of physiological models to solve problems arising in respiratory medicine.  Counsel for Professor Tehrani rightly accepted that Professor Rees gave his answers fairly and was doing his best to help the court.  I found Professor Rees to be an impressive and helpful witness.


The claimant’s action did not succeed, further the patent was declared invalid.