What Should a UK Tax Expert Witness Report Contain? A Practical Guide for Solicitors

A tax expert witness report may form part of a case where specialist tax knowledge is relevant to an issue in dispute. For solicitors, understanding the information and analysis a report may contain can help when defining the expert's instructions, identifying relevant evidence and reviewing the completed report.

The precise content of a UK tax expert witness report will depend on the nature of the dispute, the questions put to the expert and the applicable procedural requirements. A report prepared for court or tribunal proceedings should also remain within the expert's relevant area of expertise.

For background on the role of a tax expert witness and the types of matters that may involve specialist tax evidence, visit the tax expert witness guide.

This guide explains the main elements that may need to be considered when preparing or reviewing a tax expert report.

1. The Expert's Instructions and Scope

A tax expert witness report will generally be prepared in response to specific instructions. Those instructions should identify the tax issues on which specialist opinion is required.

Defining the questions for the expert

Depending on the case, the instructions may identify:

• The particular tax issue or issues in dispute
• The transactions, arrangements or periods being considered
• The questions on which specialist tax opinion is required
• The documents and information provided to the expert
• Any material factual assumptions
• The intended proceedings or forum, where known

Clear instructions can help establish what the expert has been asked to address and distinguish technical tax analysis from matters outside the intended scope.

For further information about the type of technical opinion that may be required in tribunal proceedings, see the technical tax opinion service.

Keeping the report focused

A tax expert does not necessarily need to address every issue arising in a dispute. The report will generally be more useful when it remains focused on questions that require relevant specialist knowledge.

Where an issue involves a matter ultimately for the court or tribunal to determine, the expert should distinguish that issue from the technical tax analysis they have been asked to provide.

2. The Expert's Qualifications and Relevant Experience

A tax expert witness report may include information about the expert's qualifications and professional experience relevant to the opinion being provided.

This may include:

• Professional tax or accounting qualifications
• Relevant tax experience
• Areas of technical expertise
• Experience relating to the particular tax issue
• Other professional experience directly relevant to the instructions

The information should allow the reader to understand the basis on which the expert is qualified to address the particular subject matter.

Relevant experience is generally more useful than qualifications or experience that have little connection with the issue under consideration. The tax expert witness qualifications guide provides further information about qualifications and relevant expertise.

3. The Material Considered by the Expert

A tax expert witness report should generally make clear what material the expert considered when forming the opinion.

Depending on the case, this could include:

• Contracts and agreements
• Financial records
• Tax computations
• Correspondence
• Invoices and transaction records
• Accounting information
• HMRC correspondence
• Previous tax advice
• Witness evidence
• Other documents identified in the instructions

The material considered should be sufficiently clear to allow the reader to understand the evidential basis of the expert's analysis.

Identifying material assumptions

An expert opinion may depend on particular factual assumptions. Where an assumption materially affects the analysis, it should generally be identified rather than presented as an established fact.

For example, an expert may be asked to consider the tax treatment of a transaction on the assumption that it occurred in a particular way. If that factual position is disputed, the effect of the assumption on the opinion may need to be considered.

4. The Relevant Tax Framework

A tax expert report may explain the technical tax framework relevant to the questions being addressed.

Depending on the subject matter, this could involve consideration of:

• Relevant tax legislation
• Applicable tax principles
• HMRC published material, where relevant
• Relevant accounting or financial concepts
• Relevant court or tribunal decisions
• The technical treatment of the transaction or issue in question

The extent of this explanation will depend on the complexity of the dispute and the purpose of the report.

The expert's role is generally to apply specialist knowledge to the questions within the scope of their instructions. The report should distinguish that technical analysis from legal submissions or other matters that are ultimately for the court or tribunal.

5. Analysis of the Evidence

The report should explain how the expert has considered the available evidence in relation to the questions asked.

Depending on the case, the analysis may address:

1. The relevant facts or stated assumptions
2. The applicable technical considerations
3. Evidence supporting or affecting those considerations
4. The expert's reasoning
5. The resulting opinion

The reasoning should be sufficiently clear for the reader to understand how the expert moved from the evidence and assumptions to the opinion expressed.

Dealing with incomplete information

An expert may not always have access to every document or piece of information that could be relevant.

Where information is missing, uncertain or disputed, the report should make this clear. The expert may also need to explain whether the limitation affects the analysis and, if so, how.

This can be particularly relevant where the opinion depends on facts that have not yet been established.

6. The Expert's Opinion and Conclusions

The central part of a tax expert witness report is usually the expert's opinion on the technical questions within the scope of the instructions.

The conclusions should correspond with those questions and should be supported by the analysis contained in the report.

Depending on the circumstances, the conclusions may identify:

• The opinion being expressed
• The principal reasoning supporting it
• Material assumptions
• Relevant qualifications
• Limitations affecting the opinion

A conclusion should not generally extend beyond the evidence, assumptions and technical analysis on which it is based.

Considering alternative positions

Some tax disputes involve disputed facts or more than one possible technical position. Where relevant, an expert may explain how the analysis would differ if a particular factual assumption were accepted or rejected.

This can help the reader understand the extent to which the opinion depends on the underlying factual position.

7. Sources and Supporting Material

The report may identify the sources and material relied upon in reaching the expert opinion.

Depending on the case, these may include:

• Legislation
• Court or tribunal decisions
• HMRC material
• Professional or technical publications
• Financial records
• Transaction documents
• Other material supplied as part of the instructions

References should generally be clear enough to allow the reader to understand the basis for material parts of the technical analysis.

The sources selected should be relevant to the issue being considered rather than included simply to increase the volume of supporting material.

8. Independence and the Expert's Role

Expert evidence is generally expected to be independent and within the expert's area of expertise, subject to the procedural framework applicable to the proceedings.

A tax expert's report should therefore reflect the expert's professional assessment of the relevant evidence and technical issues rather than simply adopting the position of the party who instructed them.

Where the evidence does not support a particular proposition, the expert should be able to identify that limitation.

The precise duties applying to an expert can depend on the forum and applicable procedural rules. Solicitors should therefore consider the requirements relevant to the particular proceedings when instructing and reviewing expert evidence.

The site's First-tier Tribunal tax guide provides further background on expert evidence in FTT proceedings.

9. Limitations and Qualifications

A report may need to identify limitations affecting the expert's opinion.

Examples may include:

• Missing documentation
• Unresolved factual disputes
• Reliance on stated assumptions
• Limited information available to the expert
• Issues outside the expert's specialist knowledge
• Alternative factual or technical positions that could affect the analysis

Clearly identifying material limitations can help ensure that the opinion is understood within its proper context.

10. Declarations and Procedural Requirements

A tax expert witness report prepared for formal proceedings may also need to contain particular declarations, statements or other formal elements.

The applicable requirements can vary depending on whether the evidence is being prepared for court proceedings, tribunal proceedings or another setting.

For that reason, a report should be prepared with the relevant procedural framework in mind rather than relying on a generic template without considering the circumstances of the case.

How Solicitors Can Review a Tax Expert Witness Report

When reviewing a tax expert report, solicitors may wish to consider several practical questions.

Does the report address the questions in the instructions?

The conclusions should address the issues identified when the expert was instructed. A detailed report may still require clarification if an important question within its intended scope has not been addressed.

Is the reasoning clear?

The report should provide a sufficiently understandable connection between the evidence, assumptions, technical analysis and conclusions.

Are material assumptions identified?

Assumptions that affect the opinion should be distinguishable from established facts, particularly where the factual position remains disputed.

Are relevant limitations disclosed?

The report should make clear where missing information, factual uncertainty or another limitation affects the opinion.

Does the report remain within the expert's expertise?

The report should remain focused on matters requiring the expert's specialist knowledge. Technical tax analysis should be distinguished from matters that are ultimately for the court or tribunal to determine.

Are the conclusions supported by the analysis?

The conclusions should follow from the reasoning and evidence set out in the report. Where a conclusion appears broader than the analysis supporting it, clarification may be appropriate.

When a Tax Expert Witness Report May Need Clarification

Questions can sometimes arise after a report has been prepared. For example, the instructing solicitor may identify an assumption requiring clarification, locate additional documents or need to understand how a particular part of the analysis was reached.

Whether an expert can provide clarification, amend an opinion or provide further evidence will depend on the circumstances and applicable procedural requirements.

If new evidence could affect a material assumption or conclusion, its significance may need to be considered by the expert.

Conclusion

A UK tax expert witness report may include the expert's qualifications, instructions, material considered, factual assumptions, relevant tax framework, analysis, opinion, supporting sources and applicable declarations.

For solicitors, careful instructions can help establish the questions the tax expert is being asked to address. When reviewing the completed report, particular attention may be appropriate to the expert's reasoning, assumptions, limitations and the connection between the evidence and conclusions.

The precise requirements for expert evidence depend on the proceedings and circumstances of the case. The applicable professional and procedural requirements should therefore be considered when instructing or reviewing a tax expert witness report.

Disclaimer: This article provides general information about tax expert witness reports in the UK and is not legal, tax or procedural advice. Requirements for expert evidence can vary according to the proceedings and circumstances of an individual case.

Last Reviewed: September 2026