An overview of expert evidence in litigation

Expert evidence is required in cases where help from a third party with the appropriate knowledge and experience to understand an issue is vital to a case. The types of case where expert evidence is commonplace ranges from professional negligence, personal injury, intellectual property, information technology, all the way through to shipping and building disputes.

There are some cases where expert evidence is not usually permitted or required. In judicial review and public procurement cases, where the issues relate to clear error or unfairness, expert evidence will generally be inadmissible or irrelevant due to the following reasons:

  • the limited nature of the review conducted by the Court;
  • the fact that the Court is not replacing its own opinion for that of the relevant authority involved in the case;
  • the fact that the relevant authority involved in the case is likely to be made up of experts itself or that it would have taken expert advice; and
  • such expert advice might usurp the Court’s function.

However, it should be noted that expert evidence may be admissible in cases where it is required to provide ‘technical explanations’ or where evidence is necessary and relevant to allow a Court to reach a decision on a clear error.

Instructing and retaining an expert

Finding the right expert to provide evidence is often the most important step in a case, as failure to find an appropriate expert can be catastrophic and have a direct or indirect bearing on the outcome of a case (see recent caselaw below). Many practitioners recommend that the search for an expert witness should begin as early as possible, particularly in multi-party cases.

Although the search for an expert can begin early in a case, the formal appointment of an expert should only take place after the Court has considered the necessity and scope for expert evidence, usually at a Case Management Conference (CMC). Civil Procedure Rule (CPR) 35.4 states that no expert report may be served or expert evidence used without the Court’s permission and CPR 35.1 also states that expert evidence will be restricted to that which is reasonably required to resolve the proceedings. As mentioned above, it is recommended that the search for an expert begins before the CMC, although in practice it may be difficult.

There are also various rules governing the terms of the retainer relating to the experts. It is advisable to set out the terms of the appointment of the expert in the retainer and those giving instructions to an expert should ensure that they give clear instructions. However, it is recommended that the terms of the retainer are kept separate from the instructions to the expert. This is because CPR 35.10(4) states that instructions to experts are not privileged against disclosure, but it can be argued that the retainer letter does not have to be disclosed. The same can be said of documents such as draft witness statements or other similar documents.

The terms governing the appointment of an expert should also deal with other areas of concern such as conflicts of interest, confidentiality and termination. An expert’s own standard terms of engagement can be used to govern the relationship with the instructing party. However, the solicitor should ensure that at a basic level the terms that are eventually signed also include the above provisions.

There are also various other rules, guidance documents and protocols that are relevant to the instruction of experts. These include:

  • The Civil Justice Council (CJC) Protocol on expert evidence – experts and those instructing them are expected to take into account the guidance contained in the Protocol;
  • The Court Guides – these guides supplement the CPR. There are four guides (Commercial, Technology and Construction Court (TCC), Chancery, and Queen’s Bench) and the correct one will depend on which Court is hearing the case;
  • Pre-action Protocols – if a specific pre-action protocol is relevant to the case, it is advisable to check whether it specifies what the parties should do in relation to experts; and
  • The Academy of Experts Joint Code – this is a brief document that aims to have European-wide jurisdiction on the use of expert evidence.

In terms of fees, it should be decided at the outset who (the solicitor or the client) will be primarily liable for payment of the expert witnesses fees. However, despite this, the aim will almost certainly be for all or part of the expert witness’ fees to be recovered from the opponent if the client is successful.

It should be noted that it is unlikely that the fees for an expert asked to advise during the pre-action stage will be recoverable. That is, unless the Court subsequently gives permission for that expert to give evidence during the proceedings. On this basis, it is important to warn the client ahead of time of the chances of recovering such fees to avoid any issues later on.

As a result of the changes introduced on 1 April 2013 in relation to cost estimates and cost budgeting, depending on which Court the proceedings are taking place in, it may be advisable to bring the changes to the expert’s attention at an early stage of the relationship. Additionally, it is possible that future changes may well require experts to provide timely fee estimates, which in effect will help all parties manage the expectations of costs.

In terms of liability, it is commonplace for experts (such as accountants) to request indemnities against liability for any potential claims made against them or alternatively to request the inclusion of clauses in the terms of engagement which exclude or limit their liability for such claims.

Types of expert

The main types of expert used in litigation are as follows:

  1. Expert witness – evidence given by expert witnesses can be, and usually is based on expert opinion rather than fact. An expert witness can be called on to give evidence in the form of a written report before trial or in the form of oral evidence during the trial itself. The expert witness’ primary duty is to aid the Court in its decision. This duty to the Court overrides any duty that the expert witness may have to those who are instructing or paying him/her.
  2. Expert adviser – sometimes also known as an independent expert, an expert adviser is different from an expert witness. An expert adviser provides advice to a specific party on a specialist or technical matter at any stage of a dispute or claim. The expert adviser may also assist with the formulation of the case and other tasks such as preparing witness statements and providing an assessment of the merits of a case. The most important difference between an expert adviser and an expert witness is in relation to their duties (including privilege) in communication. On this basis, it is often advisable to be careful about what an expert adviser is asked to do if there is a possibility that they may be asked to be an expert witness later on in the case. There is a risk that an expert adviser may not be able to be used as an expert witness if he or she is not considered to be independent.
  3. Single joint expert – this is an expert instructed to prepare a report for the Court on behalf of two or more of the parties (including the claimant) to the proceedings. In certain circumstances the parties to the case may agree that a single joint expert is appropriate themselves. In such cases, the Court will provide Directions that expert evidence is to be given by a single joint expert (CPR 35.7(1)). Single joint experts are typically appointed in cases allocated to the fast track, as the cost of two experts is often disproportionate to the amount at stake. In high value, multi-track cases, it may also be appropriate to have a single joint expert if the issue on which the evidence is required is not a central issue, or is uncontroversial.

The expert’s duties

The topic of an expert’s duties has been summarised in a number of cases, including in National Justice Compania Naviera SA v Prudential Assurance Company Limited (Ikarian Reefer) [1993] 2 Lloyds’s Rep 68. However, the duties are also outlined in CPR 35, Practice Direction (PD) 35 and the CJC Protocol provisions:

  1. CPR 35 – confirms (as mentioned earlier) that the expert has a duty to help the Court on matters within their expertise. This duty “overrides any obligation” to the person who instructs or pays for the expert. There is also a requirement under CPR 35.10(2) for experts to include a statement at the end of their report, which confirms that they understand their duty to the Court and that they have complied with that duty.
  2. PD 35 – confirms that an expert has the following additional duties:
  • experts and those instructing them are expected to have regard for the guidance contained in the CJC Protocol provisions;
  • expert evidence should be the independent product of the expert uninfluenced by the pressures of litigation;
  • experts should assist the Court by providing objective, unbiased opinions on matters within their expertise;
  • experts should consider all material facts;
  • experts should make it clear when a question or issue falls outside their expertise or when they are not able to reach a definite opinion; and
  • any changes in an expert’s view on any material matter should be communicated to all the parties (and the Court when appropriate) without delay.

    3. CJC Protocol provisions – section 4 of the Protocol provides further detail on the duties outlined above. Section 4 adds a reminder that experts must assist the Court in dealing with cases in accordance with the overriding principle. This part of the Protocol also makes it clear that performance of the overriding duty to assist the Courts does not impose a duty on experts to act as mediators between parties or “trespass on the role of the Court in deciding facts”. Additionally, the Protocol also confirms that experts’ reports should:

  • set out all of the material facts and any other literature or other material that was used to form their opinion;
  • indicate where the expert’s opinion is provisional or qualified; and
  • comply with the CPR or a Court Order and that any excessive delay caused by the expert can lead to their instructing parties being penalised in costs or prevented from using the expert evidence.

It is understood that the CJC Protocol is currently being reviewed by a Civil Justice Council sub-committee along with a number of pre-action protocols. However, at present there is no indication of when the amendments are likely to come into effect.

As with the explanation of the general duties, the failure by an expert to comply with the above duties has also been considered in a number of cases and it has often been found that an expert’s failure to comply with their duties has led to their evidence being rejected. This type of ruling by the Court will not always happen, but the Judge is likely to take into account any failure to comply when deciding how much weight to give an expert’s evidence.

The expert’s report

An expert’s evidence is to be given in a written report unless the Court directs otherwise (CPR 35.5(1)). Additionally, CPR 35.5(2) states that in small and fast track claims, the Court will not direct an expert to attend a hearing unless the interests of justice require it.


The rules for the form and content of the expert’s report are set out in CPR 35.10, PD 35.3 and section 13 of the CJC Protocol. The standout requirements for the report are:

  • it must be addressed to the Court, not the parties (PD 35.3.1);
  • it should be in the first person and set out the expert’s qualifications (PD 35.1.2(1));
  • it should include details of all of the information and materials that the expert relied on in producing the report (PD 35.3.2(2)) and state where the expert has relied on others’ unverified opinions;
  • it should confirm which facts within it are within the experts own knowledge (PD 35.3.2(4)) and indicate the source for all other factual information (PD 35.3.2(5));
  • any range of opinions on a matter in the report should be summarised by the expert and accompanied by an explanation of their own opinion (PD 35.3.2(6));
  • the expert should indicate within the report if an opinion submitted is provisional or qualified (PD 35.3.2(8);
  • it should include a summary of the expert’s conclusions (PD 35.3.2(7);
  • it must contain two statements (one on duties to the Court and the other on the requirements of CPR 35 and pre-action conduct) as set out in paragraph 13.5 of the CJC Protocol and also be verified by a statement of truth (CPR 35.10(2)); and
  • it must be signed by the expert.

It is common for the instructing solicitor to ask the expert to prepare a draft of the report so that they can check that the report complies with all of the above requirements and is accurate. Amendments can be made to an expert report in relation to factual accuracy and procedural compliance. However, an expert should not be asked to amend a report in a way that changes or clouds their opinion. On this basis, it is advisable to keep records of all drafts of the expert report along with a note of why any changes were made.

Expert reports are often exchanged simultaneously at the Court’s request during the CMC. However, in certain circumstances sequential exchange may be more appropriate. Most importantly, the expert’s report must be served by the deadline given by the Court. If a party is unlikely to be able to make the deadline, it is be advisable to attempt to seek an extension of time with the other side, and failing that to apply to the Court. It should be noted that the Court takes a dim view of parties who miss deadlines for the service of expert reports and as such the Court reserves the right to impose cost penalties or in serious cases reject the report.

Occasionally, it may be necessary to make changes to a report or produce a supplementary report. This often happens when new evidence comes to light after the expert report was served, where the expert missed an important point in their original report or if the opposition’s expert raises questions.

Where a supplemental report is required for new evidence or missed points, the expert is restricted to dealing with those points and as a result can only amend their report rather the rewrite it entirely. The amended report should set out the reasons for the changes and the amendments should be clearly marked.

On the other hand, if a supplemental report is required for any other reason, such as to deal with points raised by the opposition’s expert, the expert whose report is being questioned should include a short statement confirming the issues that have been agreed by the experts and then deal with the disputed points raised in turn in a supplementary report.

Evidence by experts at trial

The Court must provide permission before oral expert evidence can be given at trial. In large or complex multi-track cases, the oral evidence will typically be given at the CMC. In most other cases, expert evidence is not given until after the pre-trial checklist is filed.

In small claims cases, no expert evidence (written or oral) can be given without the Court’s permission. In such cases, the Court will not direct an expert to give evidence unless it is in the interests of justice. Additionally, oral evidence from experts at trial will be limited to one expert per party for any expert field and a maximum of two expert fields.

In order for an expert to give oral evidence, the party seeking permission from the Court should be able to show that:

  • the expert evidence is likely to have a significant impact on the outcome of the case;
  • the oral evidence from the expert is likely to assist the trial Judge;
  • there is a risk of injustice if the expert evidence is not tested at trial; and
  • the cost of calling the experts to give evidence will not be disproportionate.

During a trial, the Judge is entitled to reject the evidence of an expert. However, the Judge must have properly considered the expert’s evidence and provide an explanation as to why the evidence was rejected. In circumstances where the Judge does reject the expert evidence, it is advisable to check that there is nothing in the Judge’s evaluation of the evidence that might form the basis of an appeal.

The Jackson reforms: changes to the area of expert evidence

With effect from 1 April 2013, a number of changes were introduced that affect the rules governing expert evidence. These changes include:

  1. Cost estimates and specifying the issues for experts – parties applying for permission to use an expert must now provide a cost estimate and identify the field and issues that the expert evidence will address.
  2. Hot-tubbing – this procedure allows the Court to order that some or all of the experts from similar disciplines give their evidence at the same time.
  3. Increase to recoverable costs (small claims track) – the amount that can be recovered for experts’ fees was increased from £200 to £750 per expert.
  4. Costs and case management – new cost management rules were introduced automatically for multi-track cases (unless fixed costs apply), along with a power for the Court to apply the rules to other proceedings as well. Disproportionate costs may be disallowed or reduced, even if they were reasonably or necessarily incurred. This follows on from the amendment to the overriding objective in relation to costs. Additionally, various changes have been made to existing questionnaires and new forms introduced with specific questions about expert evidence.

Recent caselaw

The role of expert evidence in litigation has recently hit the headlines. In the UK, the High Court decision in Proton Energy Group SA v Orlen Lietuva [2006] EWCA Civ 1028 dealt with the issue of suitability of experts.

The case itself was a dispute as to whether a contract to sell a crude oil mix had been agreed on the basis on a series of email exchanges, all of which only dealt with the headline terms of the parties’ agreement.

Evidence was given from industry experts during the case as to whether such contracts were common in the oil industry and whether it was commonplace for certain terms to be agreed after the contract was concluded. At trial, the Judge found that a contract had been concluded. However, the relevant part of the case was in relation to the expert evidence given.

The Judge made two observations about the expert witnesses, which are a reminder of the importance of selecting the correct expert witness. In this case, each party called an expert witness and in his judgement, Mackie DJ criticised both parties for their choice of expert witness, but for different reasons.

The Defendant’s expert witness had a large amount of experience in the oil and gas industry advising on ‘strategic corporate decisions’ within the market. However, crucially for this case, he had no experience of trading within the oil and gas industry. The Judge commended the expert for his straightforward and honest manner. However, he noted that the expert was unable to offer any insight into whether the contract had been concluded as he did not have any experience relating to the central issue of the case. On this basis, the Judge chose not to draw any conclusions from the evidence given by the Defendant’s chosen expert.

The Claimant’s choice of expert witness was also criticised by the Judge. It became apparent that the partner of the Claimant’s solicitors firm had been paid to lecture at conferences organised by the expert’s company in the past that and they had a very strong business relationship. Although the Judge accepted that lawyers regularly use the same expert witness, he noted that in this case there was an ongoing professional connection, which meant that it would have been prudent for the party to disclose the relationship to the Court. In such circumstances, the Court could then make an informed decision as to whether it was appropriate for the Claimant to instruct the expert.

In summary, following the changes introduced on 1 April 2013 the subject of expert evidence in litigation is becoming increasingly detailed. Expert evidence can be vital to the Court’s decision and the case of Proton Energy Group SA v Orlen Lietuva is a stark example of the dangers of not fully researching an expert’s specialism or on the other hand, knowing an expert too well.