Expert witness work can offer accountants an opportunity to apply specialist knowledge in legal proceedings. But independence, preparation and a clear understanding of your duties are essential.

An expert witness is not simply an accountant who understands a technical subject. The role involves providing independent professional opinions to help a court understand matters outside its own expertise.

For accountants considering expert witness work, this distinction is fundamental. Your responsibility is not to support the party paying your fees. It is to assist the court with objective, impartial evidence.

In a webinar, forensic accountant Juan Carlos Venegas explored the responsibilities of expert witnesses, the rules governing their work and the mistakes that can undermine their credibility.

Here are the practical lessons accountants should understand before accepting an expert witness instruction.

1. Your primary duty is to the court, not your client

The most important principle of expert witness work is independence.

An ordinary witness generally provides evidence about facts. An expert witness provides an opinion based on specialist knowledge, qualifications and experience.

For accountants, this might involve financial disputes, fraud investigations, business valuations or taxation matters, depending on their expertise.

However, being instructed by a solicitor does not make you an advocate for that solicitor's client.

Your opinion must remain objective, even when your findings do not support the position of the party instructing you.

Juan emphasised that experts must avoid allowing legal teams to influence their professional conclusions.

This also means recognising the limits of your knowledge.

For example, an accountant experienced in fraud investigations should not automatically accept an instruction involving business valuation. They must first establish whether they possess the relevant specialist expertise.

Practical takeaway: Before accepting an instruction, establish whether you have the knowledge, experience and independence required to provide a defensible opinion.

2. Understand the rules before accepting an instruction

Expert witness work involves procedural responsibilities that differ from ordinary accounting engagements.

In England and Wales, Part 35 of the Civil Procedure Rules provides the framework for expert evidence in civil proceedings.

The webinar also highlighted the importance of recognising that different procedures may apply to criminal, family and tribunal proceedings.

You should therefore identify the relevant court or tribunal and understand the applicable requirements before beginning work.

This includes considering:

• The precise questions you have been instructed to address.
• Whether the subject falls within your expertise.
• The documents and evidence available.
• Any limitations affecting your conclusions.
• The requirements governing your report and declarations.

An expert who fails to understand their instructions or procedural responsibilities may face challenges to their evidence.

Practical takeaway: Treat the letter of instruction as a critical document. Review its scope carefully and clarify uncertainties before undertaking substantive work.

3. Independence matters even when both parties appoint you

One area covered in the webinar was the role of the single joint expert.

A single joint expert is instructed to provide expert evidence for more than one party in proceedings.

This arrangement does not reduce the expert's obligation to remain independent. Nor does it mean the parties must accept the resulting opinion without question.

Juan explained several practical considerations for single joint experts.

Communication should be handled transparently, with the relevant parties kept informed. Responsibility for fees should be established from the outset, alongside any applicable limits.

The expert must also remain within the agreed instructions rather than expanding the investigation independently.

Importantly, an expert's conclusions can still be scrutinised and challenged by the parties.

Practical takeaway: Agree the scope, communication arrangements and fee responsibilities before starting a single joint expert engagement.

4. Expert discussions should narrow the issues in dispute

Expert witnesses may be required to meet or discuss their findings with another expert.

The purpose is not necessarily to persuade the other expert to change their opinion. Instead, discussions help identify where professional opinions agree and where genuine disagreements remain.

A joint statement can then record the areas of agreement and disagreement, together with the reasons for any differences.

Juan highlighted several useful preparation steps:

• Review the other expert's report and the relevant evidence.
• Agree the meeting arrangements and ground rules.
• Identify the questions that require discussion.
• Ensure the relevant documents are available.
• Record disagreements clearly, including the reasoning supporting each opinion.

A well-structured discussion can help the court and the parties concentrate on the matters that genuinely require resolution.

The webinar also stressed that requirements differ between types of proceedings. Experts should check the applicable procedural rules and any court directions.

Practical takeaway: Prepare for expert discussions as carefully as you would prepare your own report. Be ready to explain both your conclusions and your reasoning.

5. Your expert report must withstand scrutiny

An expert report is more than a technical summary. It is the document through which your professional opinion is presented and examined.

Juan stressed the importance of ensuring that your report reflects your own independent analysis.

Among the matters discussed were the expert's qualifications, the basis of their opinions, the expert declaration and the required statement of truth.

The report should also make clear when a matter falls outside your expertise or when available evidence limits your conclusions.

A particularly important risk involves changes to draft reports.

During the webinar discussion, Juan distinguished between checking a report for factual errors and allowing repeated drafting to influence the expert's conclusions.

Having a report reviewed for mistakes can be useful. However, extensive revisions, particularly those affecting professional opinions, may attract scrutiny during cross-examination.

Practical takeaway: Review your report carefully for accuracy, consistency and independence. Do not allow the instructing party to determine your professional opinion.

6. Prepare for cross-examination before entering the courtroom

Producing a report is only one part of expert witness work.

You may also be required to give oral evidence and defend your conclusions under cross-examination.

Juan identified preparation as one of the most important factors in handling this responsibility.

Before giving evidence, you should know your report thoroughly, understand the supporting documents and be familiar with the relevant page references.

You should also consider the questions that might be raised about your methodology, assumptions and conclusions.

During cross-examination, the webinar recommended several practical approaches:

• Listen carefully and avoid rushing your answers.
• Ask for clarification when a question is unclear.
• Remain calm, consistent and professional.
• Explain when a simple yes-or-no answer would be misleading.
• Request time to consider unfamiliar evidence where necessary.
• Clarify any answer that may have created a misunderstanding.

Cross-examination may challenge both your findings and your credibility. That does not mean you should become defensive.

Your responsibility remains to assist the court.

Practical takeaway: Prepare to explain how you reached your conclusions, not simply what those conclusions are.

7. Recognise when your professional opinion needs to change

Expert witnesses must be willing to reconsider their conclusions when new information affects their analysis.

Changing an opinion is not necessarily evidence of poor professional judgement. The important question is whether the change is supported by evidence and handled appropriately.

An expert should not maintain a position merely because it appeared in an earlier report or supported the instructing party.

Equally, a change in opinion must not result from pressure to produce a preferred outcome.

Practical takeaway: Keep your conclusions evidence-led and address material changes through the appropriate procedural process.

Final thoughts: independence is the foundation of expert witness work

For accountants interested in expert witness work, specialist technical knowledge is only the starting point.

You must also understand your duties, follow the relevant procedural rules and communicate your findings clearly.

Throughout the webinar, Juan returned to one central message: an expert witness must remain objective and independent from the initial instruction through to the report and any oral evidence.

That principle should guide every stage of the engagement.

Watch the CPDStore webinar

For a more detailed discussion of expert witness responsibilities, single joint experts, report preparation, expert discussions and cross-examination, watch the session:

Becoming an Expert Witness: Rules and Regulations, Best Practice and Pitfalls

Presented by Juan Carlos Venegas.

Frequently asked questions about becoming an expert witness

What is an expert witness in accounting?

An accounting expert witness is a professional who provides specialist financial or accounting opinions to assist a court or tribunal.

Unlike an ordinary witness, who generally gives evidence about facts, an expert witness can provide opinions within their specialist field.

Accountants may be instructed in matters involving financial disputes, fraud investigations, taxation or business valuations.

However, an accountant should only accept instructions covering subjects in which they have sufficient expertise.

The expert's primary responsibility is to assist the court through independent, impartial professional evidence.

What qualifications do accountants need to become expert witnesses?

Accountants considering expert witness work need relevant specialist knowledge and the ability to demonstrate that they are qualified to give opinions in the subject concerned.

Professional accounting experience alone does not establish expertise in every financial discipline.

For example, experience in taxation does not automatically qualify an accountant to provide an opinion on business valuation.

The webinar emphasised the importance of working within your own specialist knowledge and explaining any limitations.

The qualifications and experience required will depend on the subject matter and the applicable legal proceedings.

What is the main duty of an expert witness?

The primary duty of an expert witness is to assist the court by providing independent, objective and impartial evidence.

This responsibility takes precedence over the interests of the party instructing or paying the expert.

An expert must base their conclusions on professional knowledge and the available evidence rather than a preferred litigation outcome.

They must also acknowledge limitations in their expertise and avoid ignoring information that could affect their opinion.

Maintaining this independence throughout the engagement is essential to the credibility of expert evidence.

What is a single joint expert?

A single joint expert is an expert instructed to provide evidence on behalf of more than one party in legal proceedings.

The expert must remain impartial and communicate appropriately with the instructing parties.

The scope of the instructions, arrangements for communication and responsibility for fees should be clear from the outset.

Although the parties share an expert, they are not required to agree with every conclusion. The expert's report may still be scrutinised or challenged.

The expert's overriding duty remains to the court rather than to either party.

Can a solicitor review an expert witness report before it is finalised?

The webinar distinguished between reviewing a report for factual mistakes and influencing the expert's professional conclusions.

A solicitor may identify factual errors or matters requiring clarification, but the expert must retain responsibility for their independent opinions.

Repeated drafting and substantial changes to conclusions can create difficulties, particularly where earlier versions become relevant during cross-examination or disclosure.

The expert should carefully consider how any review is conducted and ensure that changes remain evidence-based.

Applicable rules and disclosure obligations should be checked for the particular proceedings.

How should an accountant prepare for expert witness cross-examination?

An accountant preparing for cross-examination should thoroughly review their expert report, supporting evidence and relevant court documents.

They should understand the assumptions and methodology behind their conclusions and anticipate possible challenges.

During questioning, experts should listen carefully, answer clearly and avoid becoming defensive.

If a question is unclear, they can ask for clarification. If a yes-or-no answer would be misleading, they should explain why.

The central objective is to assist the court with accurate, independent evidence rather than to defend a particular party's position.

The contents of this article are meant as a guide only and are not a substitute for professional advice. The author/s accept no responsibility for any action taken, or refrained from, as a result of the material contained in this document. Specific advice should be obtained before acting or refraining from acting, in connection with the matters dealt with in this article. The information at the time of publishing was accurate and could be subject to final changes.