ESG: experts and extractive industries

Articles & Publications
23 January 2024

The High Court recently reiterated restrictions on the use of expert evidence, in the context of an ESG case concerning the extractive industries in Wambura & Ors v Barrick TZ Ltd & Anor (“Wambura”).[1]

The Tanzanian villager claimants’ case was that police officers had used “excessive force” against them when providing security for the defendants’ nearby gold mine. The claimants applied to adduce expert evidence on whether the defendants had adopted adequate measures to mitigate against this risk. Their application failed.

In this short note, 4 New Square Chambers’ Isabel Barter, considers: (a) the test/guidance governing the admissibility of expert evidence; (b) its application in Wambura; and (c) wider implications for extractive industry/ESG cases.

Test for permission to adduce expert evidence

CPR 35.1 provides that expert evidence shall be restricted to that which is reasonably required to resolve the proceedings. CPR 35.4 sets out the court’s power to restrict expert evidence. The burden lies on the party seeking to adduce expert evidence to persuade the court that it will assist it.[2]

Various tests and/or guidance have been put forward by the courts over the years in relation to expert evidence.  

In Re RBS (Rights Issue Litigation),[3] Hildyard J noted that CPR 35 comprises two elements: “(i) is the evidence admissible and (ii) is the evidence reasonably required to resolve the proceedings?” ([11]). Hildyard J summarised the first element as: “… whether there is a recognised body of expertise governed by recognised standards and rules of conduct relevant to the question which the Court has to decide. Unless there is, the Court should decline to admit evidence which ex hypothesi is not evidence of any body of expertise but rather the subjective opinion of the intended witness.” ([14]).

Mostyn J in GM v Carmarthenshire CC[4] at [14] stated expert evidence should be:

“of such a nature that a person without instruction or experience in the area of knowledge or human experience would not be able to form a sound judgment on the matter without the assistance of a witness possessing special knowledge or experience….”.[5]

In Kennedy v Cordia (Services) LLP (“Kennedy”),[6] the Supreme Court put forward four considerations concerning the admissibility of expert evidence:

  1. Whether the proposed evidence will assist the court in its task;
  2. Whether the witness has the necessary knowledge and experience;
  3. Whether the witness is impartial in his or her presentation and assessment of the evidence; and
  4. Whether there is a reliable body of knowledge or experience to underpin the expert’s evidence.

As to the question of what evidence is reasonably required, Warren J designed a tripartite test in British Airways Plc v Spencer[7] namely:

  1. Whether the expert evidence was necessary in the resolution of an issue. If yes, it should be allowed;
  2. If it is not necessary, will it assist the judge in determining an issue? If it would assist but it is not necessary then the court should consider point (iii) (below);
  3. Whether, in the context of the proceedings as a whole, expert evidence on that issue is reasonably required to resolve an issue.[8]

Admissibility of expert evidence in Wambura

Master Stevens rejected the claimants’ application, and in so doing stated that the courts “should not be shy about limiting the occasions” where such evidence is adduced [12].

Whether the proposed evidence would assist the court in its task

Master Stevens had to first determine what that task was, which he held was “whether or not there was an excessive use of force having regards to international standards of appropriate behaviour” [44].

  1. He concluded that the court would be able to undertake this task without expert evidence, noting that the courts had done so in Kesabo v African Barrick Gold (“Kesabo”)[9] (concerning the same North Mara mine) [44].
  2. At [45], he rejected the claimants’ submission that the relevant international standards governing the use of force were so technical that a trial judge would need assistance to interpret them.[10]
  3. He rejected the claimants’ contention that expert evidence was required because of the level of risk posed by the situation whereby police operated as part of the defendants’ security team [46].

Having failed just one of the criteria set out in Kennedy, his view was that “case law makes it plain” that the application must fail. However, he considered the other three criteria obiter.

Whether the witness has the necessary knowledge and experience

The claimants sought to rely on Mr van der Walt[11] whose expertise was said to be “security risk assessment and risk management in the extractive industries” and whom they contended was therefore “well placed to assist the court…in extractive enterprises in complex environments in Africa, focusing in particular on the integration of police into security management” [8].

Master Stevens held that it was a “huge oversimplification” to assert that experience of security management in the “extractive sector” in Africa met the court’s test of necessary knowledge and experience to assist with this particular dispute.

Whether the witness is impartial in his or her presentation and assessment of the evidence

The defendants tried to assert that Mr van der Walt’s language in his CV (e.g. the phrase “police brutality”) bespoke a certain political bias which could prejudice his evidence. Master Stevens was more lenient, saying these criticisms were “rather harsh” and no reason in themselves “to decline his proffered experience as an expert [50].  

Whether there is a reliable body of knowledge or experience to underpin the expert’s evidence

Master Stevens held that there were “no overarching published set of detailed standards, or agreed range of acceptable conduct by a security function…what is considered acceptable appears to be all fact specific against very broad generalist guidance, such that it is well within the remit of an experienced trial judge to determine the issues unaided” ([52]).

Whether the evidence was reasonably required

Was the evidence necessary?

Master Stevens held that the evidence was not reasonably required, noting (but not citing) other authorities which held that the type of expert evidence envisaged was not necessary. He observed at [54] that:

“there were no authorities in the bundle where permission had been given for an expert in risk assessment, risk management and risk mitigation regarding alleged excessive use of force by security personnel whether engaged in and around a mine, or elsewhere.”

Presumably, Master Stevens was building on other ESG/extractive industries cases, including Kesabo,[12] to all intents and purposes the same exact case concerning the same mine, the same claims and the same defendants nearly ten years ago. There Andrews J found that the question of whether the defendant’s behaviour was reasonable was for the Judge, as there was nothing that suggested a

“… body of recognised opinion exists as to what are the appropriate steps to be taken in terms of policing a mine…there is no objectively ascertainable standard or consensus against which to judge the defendants’ behaviour.”[13]

In Vilca & Ors v Xstrata Ltd & Anor (“Vilca”),[14] Foskett J, like Andrews J, found at [25] that “it would be impossible…to conclude that there was an established consensus” on what amounted to good practice in relation to security and human rights in the extractive industries.

Would the evidence be helpful?

Master Stevens noted that a proposed expert might have relevant factual evidence to give, a point raised in Vilca [26] and left open in Kesabo [15].


Wambura is a helpful reminder that the use of expert evidence should be restricted. This is true whatever the area.

In terms of extractive industry claims, Wambura makes it clear that it is very unlikely (albeit not impossible) that permission to call experts will be granted in cases concerning risk assessment, risk management and risk mitigation regarding allegedly excessive use of force by security personnel. This is particularly so given the lack of consensus about what amounts to good practice. It also serves as a reminder that any expert evidence would need to be backed by suitably specific expertise.

On the one limb where Master Stevens found against the defendants, ‘impartiality’, future claimants in ESG claims should still be wary. In applications relating to politically charged claims concerning, for example, the environment, expert academics would likely possess a CV that betrays political leaning one way or the other or, at least, it might be easy to suggest that they did.

[1] [2023] EWHC 2582 (KB).

[2] See e.g. Clarke (Executor of the Will of Francis Bacon) v Marlborough Fine Art (London) Ltd [2002] EWHC 11 (Ch); [2003] C.P. Rep. 30 at [5].

[3] [2015] EWHC 3433 (Ch).

[4] [2018] EWFC 36 (Ch), [2018] Fam. 303.

[5] Emphasis in the original.

[6]  [2016] UKSC 6, 2016 S.C. (U.K.S.C.) 59 at [44].

[7] [2015] EWHC 2477 (Ch),  [2015] Pens. L.R. 519, at [68].  

[8] As part of this, the court should consider the value of the claim and proportionality, the effect of a judgment either way on the parties, the cost of the evidence and who will pay for it, whether any delay will be caused or trial date lost, see [63] of British Airways Plc v Spencer.

[9] [2014] EWHC 4067 (QB).

[10] There were two potentially relevant standards: (1) the International Organization of Standardization (“ISO”) standards (which he held were “very generalised and written in plain non-technical language”) and (2) the UN Voluntary Principles on Security and Human Rights (“the VP”) interpretation of which had been considered to be a matter for a Judge in Vilca & Ors v Xstrata Ltd & Anor (“Vilca”) [2016] EWHC 2757 (QB) and Kadie Kalma & Others v African Minerals Ltd & Others (“Kalma”) [2020] EWCA Civ 144.

[11] The claimants’ first proposed expert was Gary White, an expert whose evidence had been rejected in the earlier case of Kesabo which concerned the same mine and allegations of excessive force.

[12] [2014] EWHC 4067 (QB).

[13] [2014] EWHC 4067 (QB), cited in Vilca at [21].

[14] [2016] EWHC 2757 (QB).

Related People

Isabel Barter

Call: 2010



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