One expert for both sides: single joint experts under CPR Part 35

Why permission comes first

A technical dispute does not create an automatic entitlement to expert evidence. CPR 35.1 restricts expert evidence to what is reasonably required to resolve the proceedings. The first question is therefore not “Which expert should we choose?” but “What issue genuinely requires expertise, and what will the evidence resolve?”

Under CPR 35.4(1), no party may call an expert or put an expert’s report in evidence without the court’s permission. That gateway applies before the report is relied on in the proceedings. Obtaining an opinion privately is not the same thing as having permission to use it.

A proportionate application starts with a disciplined explanation of need. When applying for permission, the parties must provide an estimate of the proposed expert evidence’s costs, identify the field and the issues the evidence will address and, where practicable, name the proposed expert. Permission relates only to the expert named or field identified, and the order may specify the issues to be addressed.

That structure limits the permitted evidence to the named expert or identified field. “A building expert” is less useful than defined questions about the cause of a defect and the remedial work required. Read the order and application together before drafting instructions.

The wider objective explains this control. CPR 1.1 requires cases to be dealt with justly and at proportionate cost, including saving expense and keeping the case proportionate to the money involved, its importance, its complexity and the parties’ financial positions. Expert evidence must serve that objective rather than become a parallel contest of its own.

Why the court may choose one expert

CPR 35.2(2) defines a single joint expert as an expert instructed to prepare a report for the court on behalf of two or more parties. Where two or more parties wish to submit expert evidence on a particular issue, CPR 35.7(1) allows the court to direct that the evidence be given by a single joint expert. A single report can avoid separate reports on the same issue.

The choice is contextual, not automatic. Practice Direction 35, paragraph 7, requires the court to consider all the circumstances, including the amount in dispute, the issue’s importance and complexity, whether separate experts would be proportionate, and whether one expert is likely to resolve the issue more speedily and cost-effectively. The nature of the evidence matters too. An established area of knowledge may present a different picture from an issue on which a genuine range of expert opinion is likely.

One expert is not presumed to answer every procedural need. Paragraph 7 also recognises that written questions to a single joint expert may not conclusively deal with every issue requiring testing before trial, and that a conference or a claim to privilege may make this mechanism impractical or inappropriate. A party proposing a different course should address those concrete features rather than simply prefer the idea of its own expert.

Track can also affect the starting point. For a claim allocated to the small claims track or fast track, CPR 35.4(3A) says that permission, if given, will normally be for evidence from only one expert on a particular issue. That is a restriction on the number of experts; it does not, by itself, tell the parties whether the expert must be jointly instructed.

Selecting and instructing the expert

The order is the starting point. Check the permitted field, the issues, the timetable and any direction about identity, fees or documents. Then separate the technical questions from the advocacy. The expert needs a defined task and relevant material, not a bundle arranged to persuade.

If the relevant parties cannot agree who the single joint expert should be, CPR 35.7(2) allows the court to select from a list prepared or identified by those parties, or to direct another method of selection. A sensible shortlist therefore does practical work even when agreement proves impossible. It should focus on the required expertise and capacity, not on who is thought likely to favour one side.

Practice Direction 35, paragraph 8, requires the claimant to serve on a single joint expert any order that requires an act by the expert or otherwise affects the expert. That step should happen before the instruction is treated as complete. The expert should not have to reconstruct the court’s directions from conflicting summaries.

Joint instruction also means visible instruction. Under CPR 35.8(1)–(2), any relevant party may give instructions to the expert, but that party must send a copy to the other relevant parties at the same time. If the parties cannot settle one agreed letter, the answer is not private communication: each instruction must remain transparent.

A useful instruction states the ordered issues, lists the documents, distinguishes agreed facts from disputed assumptions and asks neutral questions. Keep the exact letter and enclosures as a record of what the expert was asked and the material supplied.

The expert’s duty to the court

Joint payment does not make the expert a negotiator between the parties. CPR 35.3 requires experts to help the court on matters within their expertise, and that duty overrides any obligation to the person instructing or paying them. The same overriding duty applies although several parties share the instruction.

Practice Direction 35, paragraphs 2.1–2.3, say expert evidence should be independent and uninfluenced by litigation pressures; experts should give objective, unbiased opinions, should not act as advocates, and should consider all material facts, including those that detract from their opinions. An instruction that asks for a predetermined answer misunderstands the expert’s function.

For litigants in person, the practical response is to make the factual record clear and the questions fair. Do not suppress an inconvenient document or invite the expert to decide the legal dispute. Provide the material needed for the technical opinion, and leave the expert to reach it independently.

Questions after the report, and payment

Diarise the date the report is served. CPR 35.6 requires written questions to be proportionate. They may normally be put once only, within 28 days of service of the report, and only for clarification, unless the court gives permission or the other party agrees otherwise. The normal route is therefore a single, carefully consolidated set, not a rolling exchange.

Practice Direction 35, paragraph 6.1, requires a party sending questions directly to the expert to copy them to the other party or parties at the same time. Identify the relevant report paragraph and the point needing explanation. A focused question asks the expert to explain reasoning, terminology or an apparent omission; it does not use “clarification” as a label for a fresh report.

Under CPR 35.6(3), answers to questions properly put under that rule are treated as part of the expert’s report. Keep the questions and answers with the report so that the complete evidence can be read together.

CPR 35.8 allows the court to direct payment of the single joint expert’s fees and expenses, cap them before instruction and require some or all relevant parties to pay money into court. Unless the court directs otherwise, the relevant parties are jointly and severally liable for those fees and expenses. Read the order before assuming an equal split or relying on an informal arrangement.

Questions can generate a further charge. Practice Direction 35, paragraph 6.2, requires the instructing party or parties to pay the expert’s fees for answering questions under CPR 35.6, without affecting the court’s later decision on who ultimately bears those fees. Ask whether the original quotation covers answers and what further work will cost.

CPR 35.4(4) separately allows the court to limit the amount of a party’s expert fees and expenses recoverable from another party. Budget for the report, any permitted examination, clarification answers and further authorised work. Record the quotation, any cap, payment deadlines and responsibility for payment.

Single joint expert or assessor?

The labels are not interchangeable. A single joint expert is instructed on behalf of two or more parties, whereas an assessor is appointed by the court to assist it on a matter within the assessor’s skill and experience; under CPR 35.15, the court may direct an assessor to prepare a report or attend all or part of the trial to advise the court.

Practice Direction 35, paragraph 10.4, states that an assessor does not give oral evidence and is not open to cross-examination or questioning, although copies of any assessor’s report are sent to each party. That contrasts with the express written-question mechanism for a single joint expert. When an order uses either term, read the role and directions actually given rather than assuming the procedures are the same.