Expert evidence in a technical dispute

Technical evidence can explain why a machine failed, work was defective or a valuation differs. In civil proceedings in England and Wales, expert evidence is controlled by CPR Part 35 and requires appropriate court permission. ^[1]

Define the technical question before instruction Separate factual observations from matters requiring specialist opinion. Identify the relevant discipline, material to inspect and assumptions that need testing. An engineer should not be asked to decide a legal question about contractual interpretation.

Ask about qualifications, availability, conflicts and fees. Provide material that challenges your position as well as documents supporting it. A report based on a selective account may be unreliable and expensive to correct.

Preserve the object of the investigation Arrange access before destructive testing or remedial work. Record samples, photographs and any changes to the site or equipment. Ask the adviser how to arrange a fair inspection opportunity for the opposing party before evidence is altered.

Use a narrowly defined independent assessment where it could resolve one issue. Include report preparation, questions and possible attendance in the litigation budget. An expert's independence is essential; payment does not make their conclusion something the client can dictate.

Match the disputed issue to the appropriate discipline Describe the physical or technical question in neutral terms. A machine stopping does not by itself establish whether the cause was design, maintenance, operation or an external event. Give the proposed expert the relevant history and ask whether the issue falls within their competence. A specialist in one aspect of a system may need input from another discipline. Confirm that limitation before commissioning a broad report, so the investigation is not built around expertise that cannot answer the decisive question.

Separate observations from opinions and legal questions. The date of an inspection and a photographed crack are factual records; the cause, significance or likely development of the defect may require opinion. Whether a contract allocated responsibility is a different question for legal analysis. Frame instructions accordingly. The expert should understand what technical assistance is sought without being asked to endorse the client's legal case. This distinction makes the eventual report more useful and helps identify where further evidence, rather than stronger language, is needed.

Preserve the condition and record the investigation method Before repairs, sampling or destructive testing, identify what evidence could be changed or lost. Record the present condition through suitable photographs, measurements and contemporaneous notes, with advice on appropriate preservation. Ask how the opposing party can have a fair inspection opportunity where relevant. Keep the original records and note who handled any sample. An investigation may be technically sound but difficult to evaluate later if nobody can explain where a sample came from or what happened to the equipment before testing.

Discuss the proposed method with the expert, including its limitations and any alternatives. Identify access requirements, safety arrangements and the information necessary to interpret results. If urgent remedial work cannot wait, explain the urgency and obtain advice on proportionate evidence preservation before proceeding. Avoid presenting the need to keep a business operating as a reason to omit all documentation. A clear record of unavoidable changes can help the expert distinguish the condition originally complained of from the condition encountered at the later inspection.

Give balanced instructions and usable source material Provide the relevant records, including material that challenges the preferred explanation. Maintenance logs, earlier faults, operating instructions and correspondence about previous modifications may each matter. Identify gaps and disputed accounts rather than silently selecting only supportive documents. Ask the expert to state assumptions and to explain how a different factual premise would affect the conclusion. An opinion built on a transparent basis is easier to assess than one that sounds definite because inconvenient uncertainty was removed from the instructions.

Clarify whether the appointment is for private advice or expert evidence intended for proceedings. CPR Part 35 controls expert evidence in civil proceedings, including permission to rely on it and the expert's duty to the court. That is distinct from simply obtaining preliminary specialist advice. Discuss the intended use with the legal representative before commissioning a final report, so scope, format and independence are addressed appropriately. Do not promise the expert that a particular conclusion is required to justify the client's expenditure. ^[1]

Evaluate the report before widening the commission Read the conclusion alongside the questions asked and the limitations stated. Identify which points are answered, which depend on disputed facts and which require further work. Ask for clarification of technical language through the appropriate process rather than rewriting the expert's opinion yourself. A report may narrow possible causes without establishing one with certainty. That can still be useful if the business understands what the evidence supports and how much additional investigation would be needed to resolve the remaining uncertainty.

Plan the next decision around that uncertainty and the value of the dispute. Further testing, a meeting between specialists or questions under the applicable procedure may have different costs and purposes. Ask for an updated scope and estimate before authorising additional work. Keep the technical conclusion separate from the legal assessment of liability and loss. A well-managed commission should leave the business with an understandable answer to the technical question and a clear account of any remaining evidential limits, not merely a large report whose practical implications are unknown.