A witness is a person who gives evidence to a court or a tribunal while under oath. There are two main kinds of witnesses. A witness of fact gives first-hand facts about what they saw or did. An expert witness gives expert evidence within their area of expertise to help the court understand matters within a specialist field. Their role is to assist the court, not to argue for a party.
In construction cases, for example, expert witnesses may include contractors, developers, material suppliers, safety managers, electricians, demolition specialists and compliance professionals. Their knowledge and experience help the judge, and sometimes a jury, to understand technical issues and to reach a clear decision based on facts.
Who Can Be An Expert Witness?
An expert witness is usually someone with considerable experience, recognised qualifications or specialist knowledge in a specific field. Courts look for a person who is independent and familiar with the subject matter. The expert must be able to explain complex information in a way that the court and the parties can understand. In England and Wales, expert witnesses give evidence only with the permission of the court, and they are instructed through proper procedure rules.
Duty to the Court and Independence
An expert witness has a duty to the court that overrides any obligation to the party who has instructed or paid them. This duty to the court is continuous. It applies during preparation, during proceedings and when giving evidence. Experts must be impartial and objective. They must not act as advocates, they must not take a side in the dispute, and they must avoid any conflict of interest.
If a conflict of interest could arise, they must say so at once so the court can determine how to proceed.
Instructions and the Letter of Instruction
Experts are usually instructed by a letter of instruction. This sets out the questions to be answered, the issues in the case, any time limits and the form of the expert’s work. Clear instructions are required so that the expert knows the facts and documents to consider. The expert should acknowledge the instruction, confirm their availability, fees and terms, and confirm that no conflict of interest exists. The parties should keep the expert informed of developments in the litigation and any key dates.
What an Expert Witness Does Before The Hearing
Preparation is vital. The expert reviews relevant information, such as pleadings, witness statements, technical records and site photographs. The expert may ask for further details so that their findings and conclusions are based on a sound factual account. The expert may visit a site, carry out tests within their expertise, or review other experts’ reports. If further assistance is needed from a different field, the expert should say so and give advice about the right kind of specialist to instruct.
The Expert’s Report
The expert provides an expert report, often called the expert’s report. This document contains the expert opinion on the issues set by the instructions. It should include the expert’s qualifications, the facts and materials relied on, the methods used, and the expert’s findings, conclusions and opinion.
It should explain any assumptions, any limits on the work, and any areas outside the expert’s knowledge. It should give a clear statement of truth and comply with the procedure rules and court guidance.
The report should be written in plain language, with a view to helping the court on matters that are relevant. The expert must be open about any range of opinion in the field and must give reasons for their view. If new facts emerge, the expert may need to provide a supplemental report or an addendum. Experts are responsible for ensuring their reports remain accurate. If an error is found, the expert should correct it at once and disclose the change to the parties and the court.
Meetings of Experts and Joint Statements
Courts often order experts to meet without the parties to narrow the issues. These meetings help the court and can save time. Experts discuss the subject matter, identify where they agree and where they disagree, and produce a joint statement. This is not a negotiation. Each expert remains independent. The joint statement sets out points of agreement, points of disagreement and the reasons. This helps the judge to find the real matters in dispute.
Questions To Experts and Disclosure
After service of an expert report, the other party may put written questions to the expert on their report. The expert should answer within the time set by the rules or the court order. Answers become part of the expert evidence. Experts must keep a clear record of the materials they rely on because disclosure may be required. The expert should only deal with relevant information and keep their file in good order.
Giving Evidence at Court
When giving evidence, the expert takes an oath or affirms. They give oral evidence to explain their report and to assist the court. First there may be examination-in-chief, followed by cross examination by the other side, and questions from the judge. The expert should keep answers clear and concise, stay within their expertise, and explain any technical terms. If there is a jury, the expert must use straightforward language so that jurors can understand. The expert should be ready to explain how their conclusions were reached, the data used and why their opinion is objective.
Limits on the Role
An expert must not act as a negotiator or advocate. They must not argue the case for either party. They must not offer opinions beyond their area of expertise. They must not accept terms that depend on the outcome of the litigation.
Payment must be for the time and work done, not for success. If the expert is instructed in a criminal defence case or a civil claim, the duties are the same. The expert’s role is to assist the court, not to support a party’s interests.
Single Joint Experts and Multiple Experts
Sometimes the court orders a single joint expert who is instructed by both parties. In other cases, each party may have its own expert, but the court will expect the experts to act independently and to comply with the rules. The court can limit expert evidence to what is necessary and proportionate. The aim is to help the court reach a fair decision on the facts and the law.
Fees, Timing and Practical Points
Before work starts, the parties should agree terms of engagement in writing. This should cover rates, time estimates, payment terms and any limits on the scope of work. Experts are usually paid by the instructing party, but the court can determine who is responsible for costs at the end of the case. Experts should keep accurate time records and provide clear invoices. If more time is required, the expert should explain why and seek further instructions.
Appeals and Later Stages
If the court makes a decision and there is an appeal, the expert may be asked to give further assistance.
The expert should review any new instruction and confirm whether their earlier views still stand.
If the situation has changed, the expert should update their opinion with reasons.
Choosing The Right Expert
When you choose an expert witness, look for qualifications, relevant experience and a track record of reliable reports. Check for independence, check for a potential conflict of interest, and ensure the expert can comply with court rules and deadlines. Ask for a clear letter of instruction, set the questions that the expert should answer, and provide full and accurate documents so the expert can give a proper opinion based on facts.
Example of How Expert Evidence Helps
Imagine a building dispute about cracking in a wall. The claimant says poor materials were used. The defendant says movement in the ground is to blame. A structural engineering expert examines the site, reviews drawings and test results, and prepares an expert report. The report explains the cause of the cracking, gives a reasoned expert opinion and sets out the findings in a form the court can use. At trial, the expert gives evidence, answers questions in cross examination, and helps the court on matters that are technical. The judge uses this assistance to determine the issue and reach a decision that is fair and based on clear facts.
What Does An Expert Witness Do In Court
Expert witnesses exist to help the court. Their duty to the court comes first. They provide independent expert opinion within their expertise, based on facts, and in line with procedure rules. They must give relevant information, disclose what they rely on, and comply with instructions and court orders. When experts act in this way, they assist the court and the parties, and they help the judge to find the truth and apply the law in a fair way.
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