Economic consulting produces two very different things: commercial analysis for a client, and expert evidence for a court. The second is governed by rules that override the instructing party — CPR 35.3 states that the expert's duty to the court "overrides any obligation to the person from whom experts have received instructions or by whom they are paid". An economist who does not know that distinction is a liability.
What the work covers
The label spans quantification of loss in a damages claim, competition and market analysis, regulatory and pricing work, valuation of a business or an asset in dispute, and economic appraisal of a public sector proposal. What unites the litigation-facing parts is that the output may end up in front of a tribunal, and once it might, a different rulebook applies.
The expert's duty runs to the court
CPR Part 35 is short and worth knowing precisely.
The evidence is restricted. Rule 35.1: expert evidence "shall be restricted to that which is reasonably required to resolve the proceedings". Rule 35.4: no party may call an expert or put in an expert's report without the court's permission. Rule 35.5: the evidence is to be given in a written report unless the court directs otherwise.
The duty is to the court. Rule 35.3 makes it explicit — the duty to help the court on matters within the expert's expertise overrides any obligation to whoever instructs or pays them. Practice Direction 35 reinforces it: the evidence "should be the independent product of the expert uninfluenced by the pressures of litigation", the expert must not assume the role of advocate, and must consider all material facts including those detracting from their opinion.
Two further PD35 duties are routinely overlooked. The expert must make clear when a question falls outside their expertise or when they cannot reach a definite opinion. And where their view materially changes, they must communicate that promptly to those instructing them and, when appropriate, to the court. An economist whose analysis weakens on fresh data cannot simply go quiet.
The report is addressed to the court, not to the instructing party — PD35 para 3.1.
What a report must contain
PD35 para 3.2 sets out nine requirements. The ones that most often catch economists out:
- The substance of all facts and instructions material to the opinions expressed or on which they are based — which makes the instructing letter disclosable in substance;
- Which facts are within the expert's own knowledge, distinguished from those taken on instruction;
- Who carried out any examination, test or experiment, their qualifications, and whether it was under the expert's supervision. For a quantum model built by a team, that means naming who did what;
- Where there is a range of opinion, a summary of that range and reasons for the expert's own view. This is the requirement that defeats a report presenting one methodology as if no alternative existed;
- Any qualification where the opinion cannot be given unqualified.
The report is verified by a statement of truth confirming that the expert has made clear which facts are within their own knowledge, that those facts are true, and that "the opinions I have expressed represent my true and complete professional opinions on the matters to which they refer". Contempt proceedings can follow a false statement of truth made without honest belief in its truth.
The procedural machinery
Written questions. Under rule 35.6 a party may put proportionate written questions to another party's expert or to a single joint expert. They may be put once only, within 28 days of service of the report, and only for clarification unless the court permits otherwise. The answers form part of the report.
There is a sanction attached that clients should know about: if the expert does not answer, the court may order that the instructing party cannot rely on that expert's evidence, and cannot recover their fees and expenses from any other party.
Single joint experts. Rule 35.7 allows the court to direct that evidence on an issue be given by one expert jointly. Any relevant party may give instructions and must copy them to the others. The court can cap fees and direct payment into court — and, unless it directs otherwise, "the relevant parties are jointly and severally liable for the payment of the expert's fees and expenses".
Discussions between experts. Rule 35.12 lets the court direct a discussion to identify the issues and, where possible, reach an agreed opinion, usually followed by a joint statement of agreement and disagreement with reasons.
Two limits are precise and often misstated. The content of the discussion "shall not be referred to at the trial unless the parties agree" — which is a bar on reference at trial, not privilege, and describing it as privileged overstates it. And where experts reach agreement, that agreement "shall not bind the parties unless the parties expressly agree to be bound".
Directions. Rule 35.14 lets an expert file a written request for directions to assist them in carrying out their functions, copied to the instructing party at least 7 days before filing and to other parties at least 4 days before. It is a real route out of an impossible instruction, and it is almost never used.
The commercial work is different — and should be labelled as such
Pre-litigation analysis, deal support, pricing work and internal modelling carry none of this. They are ordinary professional engagements, and the analysis can properly be framed to answer the client's question.
The failure mode is a document that starts life as commercial advice and is later handed to lawyers as though it were expert evidence. It will not satisfy PD35 — no range of opinion, no statement of instructions, no statement of truth — and the attempt draws attention to what the earlier version said. Decide at the outset which product you are buying, and if litigation is foreseeable, commission it correctly the first time.
Choosing an adviser
Four questions do most of the work. Has this person written a report to PD35 and been cross-examined on it? Will they tell you when your case is weak, and put the contrary range in the report? Can they name who built the model? And do they understand that if their view changes, they have a duty to say so?
An economist who promises a helpful answer before seeing the data is offering something the rules do not permit them to deliver.
Acumon provides quantification, valuation and expert support through forensic accounting, valuations and forensic audit work, with financial modelling where the question is commercial rather than evidential — see also our guide to forensic consulting. If a dispute is foreseeable, the decision to commission expert-standard work should be taken before the analysis, not after it.