In  Hamad M. Aldrees & Partners v Rotex Europe Ltd [2019] EWHC 574 (TCC)  Sir Antony Edwards-Stuart expressed concern about an attack on the credibility of an expert witness.  In that case there was no evidence to support an assertion that the expert had a pre-existing relationship with the party that called it.   It is worth looking back at some those cases were impartiality is questioned.

“If questions of this sort are to be asked of an expert, they should be raised in correspondence prior to the expert giving evidence so that he and those instructing him have a proper opportunity to deal with them and, if appropriate, obtain appropriate evidence. Such questions should not be bounced on the expert in cross examination and his answers then dismissed, in effect, by a submission along the lines of “well, he would say that wouldn’t he?” “


The action concerned the quality of machines for screening and silica sand.  There was a major attack on the credibility of an expert witness.



The judge was highly critical of one aspect of the cross-examination of an expert.

  1. Professor Lieberwirth is the Managing Director (an academic position) of the Institute of Mineral Processing Machines (“IAM”), an organisation associated with the Technische Universität of Freiberg. The IAM is a research institute concerned with the development of machines and processes for the raw materials industry.
  2. In his 30 year professional career Professor Lieberwirth has toured mines and manufacturing plants throughout the world, many of which have dealt with sand processing. He started his professional career as a design and project engineer with a mining machine manufacturer and remained in the industry until he joined IAM in 2013. Professor Lieberwirth’s duties involve both teaching and providing research for the industry. He produced his report in English which he spoke fluently. He was plainly an extremely knowledgeable witness and I thought that he gave his evidence with authority and candour.
  3. The cross-examination of Professor Lieberwirth began on a very unsatisfactory note. He was questioned at some length about the association of both IAM and himself with a company called Haver. In short, it was suggested to Professor Lieberwirth that Haver had a particularly close association with IAM – and indeed that Haver had moved premises in order to be closer to the institute – and that IAM and Haver collaborated in the development of intellectual property which they may or may not be able to patent, that Professor Lieberwirth had on several recent occasions appeared on a platform or delegation with employees of Haver, that Haver had recommended Professor Lieberwirth as an expert in this case, that the CEO of Haver was the current president of an organisation called Friends of the Institute of Minerals Processing Machines, which been founded in 2006, and, finally, that Haver had entered into an arrangement with Aldrees under the terms of which a large contract would be placed with Haver if Aldrees recovered substantial damages in this litigation.
  4. Professor Lieberwirth dealt with these questions with precision and dignity. He explained that the move of Haver to Freiberg had nothing to do with any collaboration with IAM, but because its office in Meissen and was an old family owned building and that all its employees lived in Freiburg. He said that IAM had not patented anything with Haver and that in fact IAM had collaborated much more closely with several other companies, of which he named three. Professor Lieberwirth said that he frequently appeared on platforms with employees of companies in the industry and that IAM was affiliated to about 60 or 70% of the manufacturers in the field of mineral processing. He agreed that the CEO of Haver was the current head of the Friends of the Institute, which was an organisation the membership of which included about 20 companies and was concerned to raise money for the education and support of students.
  5. Professor Lieberwirth gave the name of the person who had recommended him to Aldrees as an expert, a Mr Paritzke from a company called BHS. He said that he was not aware of the contract between Haver and Aldrees and that he had no detailed knowledge of the business affairs of Haver.
  6. Whilst any party is perfectly entitled to question the independence and impartiality of another party’s expert, it seemed to me that this line of cross examination was based on little more than innuendo. For instance, there was no evidence whatever to contradict Professor Lieberwirth’s denial of any knowledge of any potential contract between Aldrees and Haver, and I consider that it was wrong for Professor Lieberwirth to be pressed about whether or not he was sure that he had not been recommended to Aldrees by Haver when he had already given the name and company of the person who had recommended him. There was no evidence of any relationship between Haver and IAM that was any different to the relationship that IAM had with several other companies in the industry.
  7. If questions of this sort are to be asked of an expert, they should be raised in correspondence prior to the expert giving evidence so that he and those instructing him have a proper opportunity to deal with them and, if appropriate, obtain appropriate evidence. Such questions should not be bounced on the expert in cross examination and his answers then dismissed, in effect, by a submission along the lines of “well, he would say that wouldn’t he?” I wish to make it absolutely clear that I can see no foundation whatever in the suggestion that there might have been some form of improper connection between Professor Lieberwirth, Haver and Aldrees, let alone one that had led him to be appointed as an expert in this case. I sincerely hope the no expert who gives evidence in this court will be treated in a similar manner in future.
  8. As an expert, I thought that Professor Lieberwirth gave his evidence in a clear and straightforward manner and on the whole I accept his evidence save where I make a finding to the contrary.


That section may need to be read again to see how serious the allegation was.  It was not simply an allegation of knowing the parties or of partiality there was an allegation that the expert was involved, somehow, in an agreement “that Haver had entered into an arrangement with Aldrees under the terms of which a large contract would be placed with Haver if Aldrees recovered substantial damages in this litigation.”

We do not know the source of that particular line of questioning.  However the facts here are very different to those in EXP -v- Barker [2015] EWHC 1289 (QB). In EXP during the course of the trial it became apparent that the defendant doctor and the defendant’s expert were well known to each other, had been professional colleagues and had written research papers together.   This information had not been given to the claimant. Indeed it appeared that references to the joint papers had been removed from the expert’s c.v.


In this case the judge dealt with the issue of the expert’s relationship with the defendant.

45.The Defendant attached a curriculum vitae to his witness statement of 10 July 2014. It showed that he had received his medical education at the teaching hospitals in Bristol and Birmingham, before he became a registrar in radiology at “Oxford RHA” in August 1984.  He remained a registrar until March 1989, when he became senior registrar in neuroradiology at the Radcliffe Infirmary, Oxford.  He remained in that position until October 1991.  He stated that he had spent four and a half years in “general radiology”, saying that:
“The Oxford course provided a wide general radiological experience as well as the specialised techniques of a teaching Hospital, the latter allowing concentrated experience of body computed tomography, ultrasound, neuroradiology, angiography and interventional radiology….”
46. As to his “neuroradiology training”, Dr Barker stated:
“The Department of Neuroradiology, Radcliffe Infirmary, provided comprehensive service for the Oxford Region.  I spent a total of nine months on rotation through the Department prior to my appointment as Senior Registrar in Neuroradiology and then two and a half years in this specialist post.  I received training in myelography, angiography, computed tomography, magnetic resonance imaging and interventional neuroradiology.”
47. In these passages Dr Barker did not mention Dr Molyneux at all. Dr Molyneux produced a curriculum vitae, as already noted, in which he stated that he had been a consultant neuroradiologist at the Radcliffe Infirmary, Oxford.
48. Someone comparing these respective CVs would reasonably infer that Dr Barker would have had contact, possibly significant contact, with Dr Molyneux from about August 1984, and in particular from about March 1989, when he became senior registrar, until October 1991 when he became a consultant neuroradiologist in Southampton. However, someone looking at the respective CVs would not know the exact nature and extent of any connection between Dr Barker and Dr Molyneux, because neither of them in their written statements condescended into setting out particulars of any such conn  On the contrary, neither referred explicitly to any such connection.
49. Mr Angus McCullough QC, on behalf of the Defendant, suggested that the respective CV’s should have put the Claimant, or at least her legal representatives and proposed experts, on notice that there was likely to have been some sort of connection, and that they ought then to have pursued the matter with the Defendant.
50. I do not accept that suggestion. In my view, the burden was fairly and squarely on the Defendant, in particular on Dr Molyneux who was to be the Defendant’s key (in the event, sole) expert witness at the trial, to state frankly, with adequate particulars, the nature and extent of any connection between Dr Barker and Dr Molyneux.
51. The Defendant knew the details; it is both fair and economical that the Defendant should disclose them. The Claimant should not be expected to engage in the time consuming detective work, the output of which might be incomplete or inaccurate, in order to ascertain the full picture bearing on Dr Molyneux’s independence as an expert witness.  Furthermore, if the Claimant had been given full particulars, the issue of Dr Molyneux’s independence could have been explored, as it should have been explored, before the trial began. [emphasis in original]
52. It emerged only in cross-examination at the trial that the connection between Dr Barker and Dr Molyneux had been lengthy and extensive.
53. Dr Molyneux had trained Dr Barker during his seven years of specialist radiology training, and in particular had trained him for two and a half years as a registrar and senior registrar in neuroradiology, including the particular area of interventional radiology in which Dr Molyneux specialised and in which Dr Barker had a special interest.  It is clear that they had worked together closely over a substantial period.  They had written together a paper for the 14th International Symposium on radiology, a paper not shown on Dr Molyneux’s list of publications, and Dr Molyneux told the Court that they might have co-operated on other papers which he could no longer specifically recall.  Dr Molyneux helped Dr Barker to obtain foreign placements:  Dr Barker had been a Visiting Fellow at the Department of Neuroradiology, University of California at San Francisco in February and March 1990; and William Cook International Fellow, Department of Neuroradiology, Sahlgren Hospital, Gottenberg, with Dr Barker taking care, in this instance, to note in his CV that this enabled him to gain further practical experience “under the supervision of Dr P Svendsen”.  Dr Barker accepted that Dr Molyneux had guided and inspired his practice, and Dr Molyneux had helped Dr Barker become a consultant in Southampton.  They had also been officers together on the committee of the British Society of Radiologists, Dr Barker having been Treasurer at the time when Dr Molyneux, being a committee member, was nominated President.
54. It also emerged that Dr Barker had suggested that Dr Molyneux should be a defence expert. He had first been asked in cross examination whether he had chosen Dr Molyneux as an expert, which he denied, and he had had to be prodded with a further question to elicit the full picture.
55. Mr McCullough QC suggested that most, if not all, of the above cast no real doubt on Dr Molyneux’s independence, because it was now in effect ancient history. I also reject that suggestion. Where a medical practitioner such as Dr Molyneux has played a relatively prominent part as mentor of another practitioner’s career, the bond may well have a very lasting effect, and it is imperative that the connection, even if well in the past, should be disclosed if the mentor is to be put forward as an independent expert witness whose evidence would benefit the person who had been under his or her tutelage.  In any event, Mr McCullough’s suggestion was wholly undercut by Dr Molyneux, perhaps in an unguarded moment, referring to Dr Barker in his oral evidence by his first name, “Simon”. I was somewhat taken aback by this use of nomenclature, because it both tended to show that traces of the relevant bond could still be found, and also that Dr Molyneux was not presenting himself as an expert having the necessary emotional distance from, and professional objectivity about, the practitioner whose competence had been called into question.
56.  In my judgment, there was in this case a very substantial failure indeed, both on the part of the defence more generally but also specifically on the part of Dr Molyneux himself, to disclose, with adequate particularity, the nature and extent of Dr Molyneux’s connection with Dr Barker, so that the Court would have a complete understanding of all matters that could realistically affect Dr Molyneux’s independence as an expert witness. That failure occurred nothwithstanding paragraph 17 of the order of Master Cook on 2 June 2014 in which he specifically directed that:
“Experts will, at the time of producing their reports, incorporate details of any employment or activity which raises a possible conflict of interest.””
“56. In these circumstances Mr Grahame Aldous QC, on behalf of the Claimant, submitted that I should entirely exclude the evidence of Dr Molyneux. I was taken to a number of authorities in support of, and in opposition to, that submission. However, those authorities have been analysed with considerable scholarship in Phipson on Evidence at paragraph 33-29, and it seems to be that at paragraph 33-30 the learned editors summarise the principles that emerge from the authorities with admirable lucidity, as follows:
“The current state of the law may be summarised by the following principles.
(1) It is always desirable that an expert should have no actual or apparent interest in the outcome of the proceedings.
(2) The existence of such an interest, whether as an employee of one of the parties or otherwise, does not automatically render the evidence of the proposed expert inadmissible. It is the nature and extent of the interest or connection which matters, not the mere fact of the interest or connection.
(3) Where the expert has an interest of one kind or another in the outcome of the case, the question of whether he should be permitted to give evidence should be determined as soon as possible in the course of case management.
(4) The decision as to whether an expert should be permitted to give evidence in such circumstances is a matter of fact and degree. The test of apparent bias is not relevant to the question of whether an expert witness should be permitted to give evidence.
(5) The questions which have to be determined are whether:
(a) the person has relevant expertise; and
(b) he is aware of his primary duty to the Court if they give expert evidence, and are willing and able, despite the interest or connection with the litigation or a party thereto, to carry out that duty. ”
(6) The judge will have to weigh the alternative choices open if the expert’s evidence is excluded, having regard to the overriding objective of the Civil Procedure Rules.
(7) If the expert has an interest which is not sufficient to preclude him from giving evidence the interest may nevertheless affect the weight of his evidence.
Even where the court decides to permit an expert to be called where his independence has been put in issue, the expert may still be cross-examined as to his independence and objectivity.”
57. The authorities emphasise the importance of disclosure, indeed early disclosure, of any conflict. The Guidance of the General Medical Council published on 25 March 2013, with effect on 22 April 2013, entitled “Acting as a witness in legal proceedings” also rightly emphasises the importance of early disclosure, as follows:
Conflict of Interest
If there is a possible conflict of interest – for example, you have been professionally or personally involved with one of the people involved in the case in the past, or you have a personal interest in the case – you must follow our guidance on conflicts of interest. “You must also make sure the people instructing you, the other party and the judge are made aware of this without delay. You may continue to act as an expert witness only if the court decides the conflict of interest will not affect the case.” (my emphasis)
58. Failure to make early disclosure may lead to the kind of chaotic situation that has arisen in this case, where the nature and extent of the conflict became clear only in the course of the trial and led to a submission, after all the evidence had been heard, that the evidence of the Defendant’s expert, upon which the defence in the event exclusively depended, should be ruled inadmissible by the Court. Failure to make early disclosure, particularly of an obvious conflict, also tends to raise a natural suspicion that the default was not inadvertent, and to reinforce the Court’s concern that the witness has, most exceptionally, become so compromised that the evidence must be altogether excluded.
59. Dr Molyneux apologised for his failure, but I must look at the issue objectively. Dr Molyneux also said that the conflict had not in any way affected his impartiality, independence and objectivity as an expert witness. He referred to other cases where he had not hesitated to state an expert opinion that was adverse to the interests of a practitioner who was known to him. I am not in a position to evaluate the strength of such a point. However, a further matter did arise which again raised doubts in my mind about Dr Molyneux’s independence in this case.
60. I have already referred to an extract of Mr Byrne’s expert report. Anyone reading the relevant passage (see paragraph 43 above) would reasonably have believed that the paper referred to was a model of scientific excellence in its day and was uncontroversial. However, “Surgical Neurology” in 1999 asked several well known vascular neurosurgeons to comment on the article published in the New England Journal of Medicine. The published response was highly critical, the dominant themes being that the study suffered from systemic bias in the selection of patients, was contrary to current orthodoxy and at odds with accepted medical practice. In January 2002 the Journal of Neurosurgery published a number of articles and editorials about the study, and the conclusions drawn contradicted those of the report, with the editorial echoing the original criticisms in 1999. The editor of Surgical Neurology in 2002 went as far as saying that the credibility of those involved in the challenged study had been “severely compromised” and that the interpretation of the retrospective arm, at least of the study, was scientifically flawed.
61. In these circumstances it was wholly unclear why Mr Byrne had referred to the study in the terms that he did and why he had made no reference at all to the criticisms mentioned above. He did not give evidence, so the mystery remained. The significance of this in the present context is that Dr Molyneux had been an executive committee member of the ISUIA and could have been expected to know of the criticisms of the study and to realise that Mr Byrne’s evidence was seriously deficient and misleading. Dr Molyneux accepted in cross examination that he had seen a copy of Mr Byrne’s proposed report that contained the relevant passage and he also agreed that the study could not accurately be described in the terms used by Mr Byrne, given the criticisms and controversy already mentioned.
62. He knew that Mr Bryne’s report was being relied upon in respect of what, until very shortly before the trial, was an important contested issue, yet Dr Molyneux did nothing at that stage to draw the attention of Mr Bryne, or anyone else, to what he knew to be the case. The justification for this appeared to be that Mr Byrne was the expert on neurosurgery, and it was not within Dr Molyneux’s remit to comment on any aspect of the neurosurgical evidence.
63. I find that explanation difficult to accept. Dr Molyneux was put forward as, and indeed is, an eminent neuroradiological expert with exceptional andextensive expertise in respect of aneurysms. He held an important position in ISUIA, and he well knew, as he admitted, that the 1998 ISUIA paper was not generally accepted in the neurosurgical community as scientifically unbiased and reliable. The issue of causation between the parties remained important. I would have expected Dr Molyneux in these circumstances to have done something to alert someone to what he knew to be the case. That failure, in my view, reinforced the concern that in this case Dr Molyneux might not have been as disengaged from the party in the litigation as he said that he had been in other cases.
64. Where does all this leave the Court? I must say that, in the light of the accumulation of facts and matters that I have set out at some length above, I came very close indeed to ruling that Dr Molyneux’s evidence was not admissible, on the ground that I could not properly have the confidence which the Court demands it should have in the impartiality and objectivity of an expert witness. However, I did hear the evidence, and the consequence of non admission would be potentially fatal for the Defendant. There is no doubt about Dr Molyneux’s expertise and competence to assist the Court on the remaining central issue.
65. I believe that I can fairly admit the evidence, but I must bear powerfully in mind, when I assess the weight that I should give to the evidence, the reservations that I retain about Dr Molyneux’s independence and objectivity in this case.”


  1. Where the core issue in a case turns, as it does here, on the court’s ability to evaluate the competing and finely balanced medical judgements of rival experts, the court’s confidence in the independence and impartiality of the respective experts must play an important role. I have to say, with considerable regret, that by reason of the matters set out earlier in this judgment my confidence in Dr Molyneux’s independence and objectivity has been very substantially undermined. On the other hand I have complete confidence in the independence and objectivity of Dr Butler, and I much prefer to accept his judgement, formed on the basis of his great experience and skill, that (i) a competent neuroradiologist would have been considerably troubled by the relevant images from the 1999 MRI scan; and (ii) would not have concluded that those images could be prudently and adequately explained by “normal brain anatomy”, contrary to Dr Monlyneux’s view; and (iii) would have concluded that the images did show the presence of an aneurysm.


The defendant appealed the trial judge’s findings – to no avail in EXP -v- Barker [2017]  EWCA Civ 63 Lord Justice Irwin stated:-

  1. In considering Grounds 3 to 5, the starting point is to identify what the judge decided. He considered that the witness had so compromised his approach that the decision to admit his evidence was finely balanced, and that the weight to be accorded to his views must be considerably diminished. In my view he was fully entitled to take that view. Indeed, had he decided to exclude Dr Molyneux’s evidence entirely, it would in my view have been a proper decision. Our adversarial system depends heavily on the independence of expert witnesses, on the primacy of their duty to the Court over any other loyalty or obligation, and on the rigour with which experts make known any associations or loyalties which might give rise to a conflict. Dr Molyneux failed to do so here, despite an express direction to that effect. Indeed, the omission of mention of papers co-authored with Dr Barker points in the other direction.


In  Thefaut -v- Johnson [2017] EWHC 497(QB) Mr Justice Green suggested that the issue of knowledge of the parties should be dealt with expressly in the expert’s own report.


(iv) Mr Peacock (returning fire) launched an attack on the professionalism of Mr Gullan upon the basis, inter alia, that he had failed in his report to record his prior knowledge of Mr Johnston as a colleague on various professional bodies and his regard for Mr Johnston as a surgeon of repute and skill. This was an omission going to his impartiality. He also attacked Mr Gullan upon the basis that although the issue of the findings by Mr Samandouras had been an important part of the litigation from the date of the Letter of Claim he had more or less ignored it and only really engaged with it for the first time when he gave oral evidence. He also attacked Mr Gullan for not appearing to have been aware of the actual evidence that Mr Samandouras gave in the witness box, which preceded his own evidence.
(v) In the event I took the course that I should simply listen with care to the expert evidence given by both of these experts and to the extent that there was a dispute between them I would then bear in mind any criticisms of their professionalism which I thought well founded and relevant in forming my view on the issues in dispute. My ultimate conclusion was that both experts acted properly in the giving of their evidence. I have not felt the need to discount their views on the basis of any want of professionalism. I would however make one observation. In the specialist field in issue there are a relatively small number of surgeons. They tend to know, or know of, each other, especially if they have been in practice for many years and have had prior involvement with each other as colleagues serving in the various specialist professional bodies. In such circumstances there is a high probability that when one of this select group is instructed to act as an expert in a case he or she may know of the Defendant either personally or by repute. This was the case of Mr Gullan in relation to Mr Johnston. He knew him both from co-participating in professional bodies and by repute. This did not in my judgment necessarily mean that he could not give expert evidence in the case. He was not so close to Mr Johnston that, objectively speaking, his independence was compromised. But it is my view that Mr Gullan would have been far better to get out in the open his personal knowledge of Mr Johnston. A concise but accurate and comprehensive paragraph in his report setting out the bare facts of his knowledge of Mr Johnston would have sufficed. This would have taken much of the sting out of the cross examination which did, I am bound to say, leave Mr Gullan feeling and sounding defensive. The issue here is the appearance of bias. The inevitable questions in cross examination which followed from the omission were along the lines that Mr Gullan was advancing a view which was tailored to support a fellow professional who was in a predicament, and hence lacked objectivity. If this had in fact been Mr Gullan’s intent and object when giving evidence it would have struck at the very heart of his professionalism and objectivity and it could have rendered his evidence inadmissible: see, e.g. EXP v Dr Charles Simon Baker [2017] EWCA Civ 63 at paragraph [49] per Irwin LJ. As I have observed I do not accept that Mr Gullan gave his evidence other than objectively and independently.”