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Expert Witnesses - Impartiality and Balance

Special Reports

by Ben Zielinski - Senior Associate Shoosmith LLP

In two recent but very different cases, there have been unusually strong criticisms of expert witnesses. They highlight the need for any expert witness to be seen to be independent and impartial and for their evidence to be balanced and not one-sided.

Evidence from expert witnesses plays a crucial role in determining many disputes in different fields. For example, in personal injury cases, evidence from a medical practitioner will be required. Or in a commercial action where there are technical issues in question, the court may need evidence from an expert in the relevant field. Without experts to explain the medical, scientific or technical matters, a judge may be unable to understand properly significant aspects of the case and make appropriate findings about them.

In our adversarial system of litigation, it is for each party to choose and instruct their own experts and adduce evidence from them. A party will naturally want their own expert’s evidence to support their position. Therefore, a party will generally only produce expert reports and call as witnesses, experts whose evidence is going to help that party’s position. However, if an expert is not impartial or gives evidence that appears one-sided, the evidence, although supportive of the party’s position, may turn out to be little or no worth, as demonstrated by two recent cases.

Armstrong v ERS Syndicate Management Ltd – independence and impartiality

The first case, Armstrong v ERS Syndicate Management Ltd, was a low value personal injury claim. The pursuers relied on the evidence of a medical expert with respect to the extent of their injuries. They were awarded damages based on that evidence. The defenders appealed, arguing that the expert evidence should have been found inadmissible or, alternatively, should have been given no weight. The main reason was that the expert’s independence and impartiality was questionable because he had agreed to act of contingency basis, meaning that he would only get paid if the claims were successful. The Sheriff Appeal Court had little hesitation upholding this appeal and finding the expert’s lack of independence and impartiality rendered their evidence inadmissible.

This resulted in the pursuers losing those elements of the damages awarded to them that were reliant on the expert’s evidence.

Agilisys Ltd v CGI IT UK Ltd – balanced approach

The case of Agilisys Ltd v CGI IT UK Ltd was a very different type of case. A commercial action in the Court of Session, it concerned the termination of a subcontract for the provision of information technology services to a significant public sector client.

The parties, the main contractor and sub-contractor, were in dispute about a number of issues that boiled down, broadly speaking, to which party was in breach of its obligations and responsible for various delays. Each party relied on the evidence of an expert witness. Neither expert’s independence was in question. However, the judge, Lord Bannatyne, formed a markedly different view of the two experts and their evidence.

Lord Bannatyne criticised the evidence of CGI’s expert witness in unusually direct terms. He stated: “I have come to the view that his evidence was onesided. His approach was I believe not balanced. In addition for various other reasons I believe his evidence was not acceptable.” Over the subsequent eight pages of his opinion, the judge set out numerous matters that had led him to that conclusion. He highlighted, in particular, the expert’s failure to consider whether CGI might have breached any of its obligations. It is also noted that, on one occasion, when faced with the realisation during cross-examination that part of his evidence had not in fact helped CGI, the expert switched from one position to another. This was described as “highly unimpressive in the context of someone who is being offered as giving expert evidence.”

By contrast, Lord Bannatyne noted that Agilisys’s expert “looked at the responsibilities of both CGI and Agilisys” and was “prepared to make criticisms of Agilisys”, which he said were “examples of the essential balance in her approach”. Given his contrasting impressions of the two experts, it is unsurprising that, where their evidence differed, the judge largely accepted the evidence of Agilisys’s expert and rejected that of CGI’s.


Expert evidence is critically important to many cases. When that is the case, parties need to make sure they have experts whose evidence supports their case. However, as these two cases show, it is not enough to have an expert who will give helpful evidence. The expert must be independent and impartial and their evidence should be balanced and not one-sided. Otherwise, the expert’s evidence may be given little credence or even, if the expert lacks independence, be held inadmissible.

This document is for informational purposes only and does not constitute legal advice. It is recommended that specific professional advice is sought before acting on any of the information given.

About the Author

Ben Zielinski

Senior Associate

Ben is a senior associate in Shoosmiths’ dispute resolution team. Ben specialises in commercial disputes and is based in our Edinburgh office. He is qualified as a solicitor in both Scotland and England & Wales. Ben advises on a wide variety of commercial disputes including, in particular, information technology and energy sector matters.

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