Evidence and disclosure - Opinion evidence and duties of exp...

Learning Outcomes

This article outlines the rules relating to opinion evidence and the duties of expert witnesses in civil proceedings. It covers the general inadmissibility of opinion evidence, the exceptions for lay witnesses and experts under the Civil Evidence Act 1972, and the specific requirements for expert evidence under CPR Part 35. After reading this article, you should understand the overriding duty of experts to the court, the procedures for instructing experts, the content requirements for expert reports, and the rules governing discussions between experts and single joint experts. This knowledge is essential for tackling SQE1 questions on evidence.

SQE1 Syllabus

For SQE1, you are required to understand the principles governing the admissibility and use of opinion evidence, particularly expert evidence, in civil litigation. This involves familiarity with the relevant provisions of the Civil Evidence Act 1972 and CPR Part 35. You will need to apply these rules to practical scenarios, identifying when expert evidence is required, the duties experts owe, and the procedures for managing expert evidence effectively, with a focus on the following syllabus points:

• the general rule regarding the inadmissibility of opinion evidence
• the exceptions for lay witness opinion and expert opinion evidence
• the court's power to control and restrict expert evidence under CPR Part 35
• the overriding duty of an expert witness to the court
• the requirements for the form and content of an expert's report
• the procedure and purpose of discussions between experts
• the circumstances in which a single joint expert may be instructed.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. True or False: Witnesses in civil proceedings are generally permitted to give their opinion on matters relevant to the case.
2. Under CPR Part 35, what is the expert's overriding duty?
3. Which ONE of the following statements about Single Joint Experts (SJEs) is correct? a) An SJE is instructed by only one party but prepares a report for all parties.
   b) The court cannot direct the use of an SJE if the parties object.
   c) An SJE's duty is primarily to the instructing parties who share the costs.
   d) The court may direct that evidence on a particular issue is given by an SJE where two or more parties wish to submit expert evidence on that issue.
4. Within how many days of service of an expert's report can a party put written questions to the expert for clarification?

Introduction

In civil litigation, the general rule is that witnesses should give evidence of facts they personally perceived, not their opinions. The court draws inferences and conclusions from the facts presented. However, there are specific exceptions where opinion evidence is admissible, most notably evidence given by experts. Understanding when opinion evidence is allowed, particularly the rules governing expert witnesses under CPR Part 35, is essential for managing the evidential aspects of civil claims.

Opinion evidence and expert evidence sit at the intersection of evidential admissibility and case management. The Civil Evidence Act 1972 provides statutory gateways through which limited lay opinion and qualified expert opinion may be received. CPR Part 35 and its Practice Direction regulate whether expert evidence should be permitted at all, in what scope, and in what form, reflecting the overriding objective and proportionality. Appreciating both strands—admissibility and control—will allow you to analyse whether expert opinion is (a) necessary to assist the court, and (b) presented in a way compliant with the rules.

The General Rule Against Opinion Evidence

Witnesses are typically confined to stating facts based on their direct knowledge or perception. Their role is not to offer interpretations, conclusions, or opinions on those facts, as this function belongs to the court. This rule ensures that the court bases its judgment on factual evidence rather than potentially biased or unqualified interpretations.

However, the strict application of this rule can sometimes make it difficult for a witness to convey their observations effectively. Consequently, the law recognises limited exceptions. The law therefore tolerates opinion where it is simply shorthand for factual description (for example, that someone “looked unwell”), and permits expert opinion where technical or specialist knowledge is necessary to assist the court to reach its own conclusion.

Exceptions to the General Rule

The Civil Evidence Act 1972 provides statutory exceptions allowing opinion evidence in specific circumstances from lay witnesses and, more significantly, from expert witnesses.

Lay Witness Opinion

Section 3(2) of the Civil Evidence Act 1972 permits a lay witness (a witness who is not testifying as an expert) to give an opinion if it is stated "as a way of conveying relevant facts personally perceived by him". This exception allows witnesses to express opinions that are essentially summaries of their sensory perceptions, where stating the raw facts alone would be impractical or less informative.

Key Term: lay witness
A witness giving evidence based on facts they have personally perceived, who is not testifying in the capacity of an expert.

Common examples include:

• Speed (e.g., 'The car was travelling very fast').
• Age (e.g., 'He looked about 30 years old').
• Weather (e.g., 'It was a cold day').
• Emotional state (e.g., 'She seemed very upset').
• Sobriety (e.g., 'He appeared drunk').
• Identification or recognition based on familiarity (e.g., 'I recognised the handwriting' or 'I recognised his voice').

In these instances, the opinion is admissible as evidence of the facts perceived by the witness. The weight given to such opinions will depend on the circumstances (such as the witness’s opportunity to observe) and the witness’s basis for forming that opinion. It remains open to the opposing party to cross-examine on the specifics supporting the opinion—for example, distance, lighting, and duration of observation—to test reliability.

Expert Opinion Evidence

The primary exception to the rule against opinion evidence concerns experts. Section 3(1) of the Civil Evidence Act 1972 states:

"[...] his opinion on any relevant matter on which he is qualified to give expert evidence shall be admissible in evidence."

This allows individuals with specialised knowledge, skill, or experience to provide opinions on matters falling within their field of specialization, where such opinions are necessary to assist the court in understanding complex issues beyond its ordinary knowledge and experience.

Key Term: expert witness
A person instructed to give or prepare expert evidence for the purpose of court proceedings, based on their specialised knowledge, skill or experience (CPR 35.2).

Expert evidence might be required on issues such as medical causation, the valuation of property, engineering defects, or forensic accounting. The court relies on expert opinions to understand technical or specialised matters relevant to the dispute. Admissibility is only the starting point: permission under CPR 35 is usually required to rely on expert evidence at all, and the court will limit expert involvement to what is reasonably required to resolve the proceedings. It is not sufficient that expert evidence would be “helpful”; it must be necessary in the sense of assisting the court on matters outside ordinary judicial experience, and proportionate to the issues, sums and complexity involved.

Expert Evidence Under CPR Part 35

CPR Part 35 governs the use of expert evidence in civil proceedings. Its aim is to ensure that expert evidence presented to the court is independent, relevant, and proportionate to the issues in dispute.

Duty to Restrict Expert Evidence

Reflecting the overriding objective, CPR 35.1 imposes a duty on the court to restrict expert evidence "to that which is reasonably required to resolve the proceedings." This means the court controls the extent and nature of expert evidence permitted. The court’s case management powers allow it to:

• refuse permission for expert evidence altogether
• confine expert evidence to specified disciplines or issues
• limit the number of experts or direct that evidence be provided by a single joint expert
• regulate the manner of giving expert evidence (e.g., by written report only, by concurrent evidence (“hot‑tubbing”), or by video link)
• impose timetables and page limits to ensure proportionality.

The key question when considering expert evidence is necessity and proportionality, not usefulness. In lower-value claims, or where the facts can be proved without technical opinion, permission may be withheld to avoid cost and delay.

Permission of the Court

A party cannot rely on expert evidence without the court's permission (CPR 35.4(1)). When applying for permission, the party must identify the area of specialization required, the issues the evidence will address, and if practicable, the name of the proposed expert. An estimate of the costs must also be provided. Permission, if granted, relates only to the expert or field identified and may specify the issues to be addressed.

In practice, details about proposed expert evidence are usually provided in the Directions Questionnaire and, if necessary, developed at a case management conference. The court may:

• grant permission for one or more experts in specified fields
• grant permission only for a single joint expert
• refuse permission in whole or in part, for example confining expert evidence to quantum only
• require simultaneous or sequential exchange of reports and/or direct a meeting of experts.

If a party later wishes to rely on expert evidence beyond the scope of what was permitted, a further application will be required, with full justification and an updated cost estimate.

Overriding Duty to the Court

The most fundamental principle governing experts is their overriding duty to the court. CPR 35.3 states:

"(1) It is the duty of experts to help the court on matters within their specialization.
(2) This duty overrides any obligation to the person from whom experts have received instructions or by whom they are paid."

Key Term: overriding duty
The primary duty of an expert witness, stated in CPR 35.3, to help the court on matters within their specialization, which takes precedence over any obligation to the instructing party or payor.

This means experts must provide objective, unbiased opinions regardless of the perceived interests of the party instructing them. Their role is to assist the court, not to act as an advocate for a party. An expert who strays into advocacy, suppresses unfavourable points, or fails to acknowledge contrary opinions risks having their evidence given little weight, and may face judicial criticism and costs consequences.

Instructing Experts and the status of instructions

Expert instructions are not privileged in the sense that the “substance of all material instructions” must be set out in the expert’s report (CPR 35.10(3)). CPR 35.10(4) and Practice Direction 35 recognise, however, that actual correspondence and documents containing instructions need not routinely be disclosed. The court will only permit cross-examination or disclosure about the expert’s instructions if there are reasonable grounds for considering the statement of instructions in the report to be inaccurate or incomplete. The practical implications are:

• assume the content and tone of your instructions may be scrutinised
• ensure instructions are accurate, balanced and disclose all material facts (including those adverse to your case)
• avoid inviting the expert to argue the case or to omit unfavourable points; this conflicts with the expert’s duty and will undermine credibility
• provide the expert with the statements of case, relevant documents and a clear list of questions, issues and assumptions to address.

It is standard practice for letters of instruction to remind experts of their overriding duty and the content requirements for reports.

Content of Expert Reports

Expert evidence is usually given in a written report (CPR 35.5). Practice Direction 35 sets out detailed requirements for the content of an expert's report (PD 35, para 3.2), which must include:

• details of the expert's qualifications
• details of any literature or material relied upon
• a statement setting out the substance of all material instructions
• a clear statement of facts or assumptions the opinion is based on, identifying facts within the expert's own knowledge
• details of any examination, measurement, test, or experiment conducted, stating who carried it out, their qualifications and whether it was under the expert’s supervision
• a summary of the range of opinions (if applicable) and reasons for the expert's own opinion
• a summary of the conclusions reached
• if the expert is not able to give an opinion without qualification, state the qualification and what would enable a firm conclusion (e.g., further tests, data)
• a statement that the expert understands and has complied with their duty to the court and is aware of Part 35, PD 35 and the Guidance for the Instruction of Experts in Civil Claims 2014
• a statement of truth verifying the report.

In addition, a report should be addressed to the court, be self-contained, and written in a form intelligible to a lay audience. Where appropriate, photographs, plans, appendices and calculations should be annexed. Experts should make clear where they defer to other disciplines and should not opine outside their field.

Written Questions to Experts

A party may put written questions to an expert instructed by another party or to a single joint expert about their report (CPR 35.6). These questions:

• must be for the purpose of clarification only
• must be proportionate
• must be served within 28 days of service of the report, unless the court orders otherwise
• become part of the report once answered.

Questions are not a vehicle for cross‑examination, nor for seeking to re‑open the scope of an expert’s instructions. If a party attempts to go beyond clarification, the expert can indicate that the question is outside the scope of clarification, or the parties can seek case management guidance. Where a party fails to serve answers, or answers are materially inadequate, the court may direct that the expert attend for oral evidence, may limit reliance on the report, or make an appropriate costs order to address any prejudice.

Discussions Between Experts

The court may direct experts from similar disciplines to discuss the expert issues in the proceedings (CPR 35.12). The purpose of these discussions is to:

• identify and narrow the issues
• reach agreed opinions where possible
• clarify the basis of any continuing disagreement.

These discussions are typically without prejudice and legal representatives do not attend unless agreed by the parties or ordered by the court. Following the discussion, the experts must prepare a joint statement setting out the issues on which they agree and disagree, with summaries of their reasons for disagreement. Parties must not instruct experts to avoid reaching agreement. A joint statement does not bind the parties unless they expressly agree, but it will usually define the expert issues for trial and may significantly reduce hearing time.

Where the court directs it, experts can give concurrent oral evidence at trial (sometimes called “hot‑tubbing”), allowing the judge to explore areas of agreement and disagreement in a structured, comparative way. This is a case management tool directed at efficiency and may be particularly useful in technical disputes.

Single Joint Experts (SJE)

The court has the power to direct that evidence on a particular issue should be given by one expert jointly instructed by the parties (a single joint expert or SJE), rather than each party instructing their own expert (CPR 35.7).

Key Term: single joint expert (SJE)
An expert instructed to prepare a report for the court on behalf of two or more parties to the proceedings (CPR 35.2).

The court will consider instructing an SJE particularly where the issue is not complex or the amount in dispute is relatively small, aligning with the overriding objective of saving expense and dealing with cases proportionately. This is the usual approach in fast track cases. If parties cannot agree on the identity of the SJE, the court may select one from a list provided by the parties or direct another method of selection.

Parties may put written questions to an SJE within the 28‑day period, and either party may, with permission, cross‑examine the SJE at trial. Where an SJE’s conclusions are challenged, a party may seek permission to rely on their own expert in addition, but will need to persuade the court that separate expert evidence is reasonably required (for example because the issue has proven more complex than anticipated). The court may also grant permission to obtain an advisory report, solely to assist with questions to the SJE or cross‑examination, without giving permission to rely on that advisory report as evidence.

Changing or replacing an expert

Once a party has served an expert report, it will usually need the court’s permission to rely on a different expert in the same discipline. The court’s primary concern is fairness and the integrity of the process. Permission is often conditional on disclosing the first expert’s report (even if unfavourable), so that the other parties and the court can see what has changed. Where experts have already discussed issues and produced a joint statement, the court will be slow to allow a “second bite” unless truly justified. Early and transparent case management engagement is therefore essential if a party’s confidence in its expert is lost.

Scope of oral evidence

In fast track cases, the court often directs reliance on written reports only, with no attendance by the expert at trial, unless justice requires oral evidence. In multi‑track cases, experts commonly attend for cross‑examination, but the court may regulate the time, limit the issues to be covered, or adopt concurrent evidence procedures to focus the evidence efficiently.

Worked Example 1.1

In a claim concerning alleged defective building work valued at £20,000, the Claimant (C) wishes to rely on a structural engineer's report. The Defendant (D) also wishes to rely on evidence from a structural engineer. The case has been allocated to the fast track. What direction is the court most likely to make regarding expert evidence?

Answer:
Given the value of the claim and its allocation to the fast track, the court is most likely to direct that evidence from a structural engineer be given by a single joint expert (SJE), unless there is a good reason not to do so (PD 28, para 3.9). This promotes proportionality and efficiency. The court may select the SJE if the parties cannot agree.

Exam Warning

Remember that an expert's duty is to the court, not the instructing party. An expert who appears biased or acts as an advocate for their instructing party risks having their evidence given little or no weight by the court, and may face criticism. Ensure any expert you consider instructing understands their overriding duty.

Consequences of Failing to Disclose an Expert's Report

A party who fails to disclose an expert's report cannot use the report at trial or call the expert to give oral evidence unless the court gives permission (CPR 35.13). This emphasizes the importance of complying with court directions for the exchange of expert evidence. The court will apply the relief from sanctions framework if late service is explained and justified, but if permission is refused the party may be debarred from relying on expert opinion at all. Even where permission is granted, costs consequences often follow, and the trial timetable may be adjusted to prevent prejudice.

Worked Example 1.2

A Claimant in a personal injury claim serves their medical expert's report late, missing the deadline set by the court's directions order. The Defendant objects to the Claimant relying on this report at trial. What must the Claimant do?

Answer:
The Claimant must apply to the court for relief from sanctions under CPR 3.9. The court will consider the Denton criteria: the seriousness and significance of the breach, the reason for it, and all the circumstances of the case, including the need for litigation to be conducted efficiently and at proportionate cost, and the need to enforce compliance with rules and orders. The Claimant will also need the court's permission under CPR 35.13 to rely on the late report.

Worked Example 1.3

In a multi‑track professional negligence claim, both parties seek permission for their own accountancy experts on liability and quantum. The pleaded issues on liability are narrow and largely documentary; quantum turns on straightforward arithmetic and established discount rates. What is the likely outcome of the applications?

Answer:
The court is likely to refuse permission for separate liability experts as not reasonably required and potentially refuse expert quantum evidence if it considers that the court can determine quantum without expert opinion. Alternatively, the court might confine expert evidence to a single joint expert on quantum only. The focus will be on what is reasonably required and proportionate to resolve the proceedings.

Worked Example 1.4

After exchanging engineering reports, Party A wishes to ask detailed written questions seeking new calculations on issues not addressed in Party B’s report and outside the 28‑day period. Party B objects. What should Party A do?

Answer:
Party A should seek the other party’s agreement or apply for the court’s permission to put out‑of‑time questions, explaining why the questions are confined to clarification and why they are necessary and proportionate. If the questions go beyond clarification, the court is likely to refuse permission and direct that any expansion be addressed by case management (e.g., supplemental reports or expert meetings), with costs consequences to reflect any unnecessary proliferation.

Worked Example 1.5

A party served an unfavourable orthopaedic report and now wants to instruct a different orthopaedic expert to rely on a fresh report at trial. What conditions is the court likely to impose if permission is granted?

Answer:
Permission is likely to be conditional on disclosing the first orthopaedic report to the other parties (to prevent “expert shopping” without transparency), adherence to the existing timetable (or any necessary adjustments), and costs orders to ensure no prejudice is caused. The court will require clear reasons why a change of expert is necessary.

Revision Tip

Focus on understanding the expert's overriding duty to the court (CPR 35.3) and the court's power to control expert evidence (CPR 35.1 and 35.4). These are fundamental principles frequently tested in SQE scenarios involving experts.

The General Rule Against Opinion Evidence (expanded)

Although the article above sets out the rule and its exceptions, it is worth reinforcing the practical boundaries between fact and opinion:

• A witness can describe what they saw, heard or felt, and sometimes that necessarily involves a shorthand opinion (“looked intoxicated”, “sounded distressed”). This is admissible because it conveys the direct perception.
• A witness cannot usurp the court’s role by expressing conclusions on ultimate issues (“it was negligent”, “the speed was too fast for the conditions”). Even an expert should frame opinions in terms that assist the judge, not instruct the judge on law or ultimate findings.
• Where the line is blurred, the remedy is almost always one of weight, not admissibility. The judge will evaluate the contextual basis for the opinion.

Admissibility and management: how the strands interact

Two questions arise in sequence:

• Is the opinion admissible? For lay opinion, s3(2) of the 1972 Act applies; for expert opinion, s3(1) applies.
• Should the court allow the opinion to be adduced and, if so, in what form? CPR Part 35 empowers the judge to confine or exclude expert evidence even if admissible in principle. This control ensures proportionality and prevents expert evidence becoming a platform for advocacy.

Courts are robust in applying case management controls to expert evidence. Directions may include simultaneous exchange (to avoid tactical sequencing), limits on report length, mandatory expert discussion and joint statements, and, where appropriate, evidence by video link or in concurrent sessions.

Practical guidance on expert engagement

To ensure compliance and credibility:

• Select an expert based on genuine competence, independence and clarity of communication, not on perceived alignment with your case.
• Provide balanced instructions, with full disclosure of material facts and documents, including adverse points. Invite the expert to identify any further information required.
• Remind the expert to identify assumptions made and to state any qualifications to their opinion.
• Diarise key dates: exchange of reports, the 28‑day window for written questions, the expert meeting, joint statement deadline, and (if directed) the lodging of an agreed issues list for experts.
• Prepare for expert meetings collaboratively. Parties should avoid influencing content; lawyers should not attend unless the court orders or parties agree. After the meeting, promptly review the joint statement to plan any consequential case management steps.
• Anticipate costs: expert fees, tests, site visits and conferences with counsel must be budgeted and proportionate. The court will expect costs estimates at permission stage and may disallow excessive expert expenditure.

Key Point Checklist

This article has covered the following key knowledge points:

• Opinion evidence is generally inadmissible in civil proceedings, with exceptions for lay witness perceptions and expert opinions.
• Expert evidence requires the court's permission and is restricted to that reasonably required to resolve proceedings (CPR 35.1, 35.4).
• An expert's overriding duty is to the court, helping it on matters within their specialization (CPR 35.3).
• Expert reports must comply with the form and content requirements of PD 35 and be addressed to the court, with a compliant statement of truth and duty statement.
• Parties can put written questions to experts for clarification within 28 days (CPR 35.6), and answers form part of the report.
• The court may direct discussions between experts to narrow issues and require a joint statement (CPR 35.12); legal representatives do not normally attend.
• The court can order evidence to be given by a single joint expert (SJE) (CPR 35.7), which is common on the fast track, and will balance complexity and proportionality.
• Instructions to experts must be summarised in the report; cross‑examination on instructions is only permitted where there are reasonable grounds to consider the summary inaccurate or incomplete.
• Replacing an expert after service generally requires permission and disclosure of the first report; the court will guard against expert shopping.
• Failure to comply with expert directions (including late reports) risks exclusion of the evidence and adverse costs unless relief from sanctions is granted.

Key Terms and Concepts

• lay witness
• expert witness
• overriding duty
• single joint expert (SJE)