Expert evidence at a planning inquiry: duties and scope

Expert witness planning inquiry duties start from a principle that catches out people who have only written application documents: your duty is to the inspector, not to the client paying you. You are there to give your honest professional opinion on matters within your expertise, and to say so even where the answer damages the case. The client's advocate makes the argument. You provide the evidence the argument rests on.

Everything else follows from that. Structure, scope, concessions and costs risk are all consequences of it.

The witness's duty to the inspector rather than the client

The duties expected of expert witnesses in English proceedings are well established and the planning system applies them in substance. Evidence should be the independent product of the witness, uninfluenced by the demands of the litigation. It should state the facts and assumptions it rests on. Where an opinion is not properly researched, or the witness cannot assert that it is correct, that has to be stated. And if a witness changes their view after exchanging proofs, the change must be communicated without delay.

Professional institute rules add to this. Surveyors have a practice statement on acting as expert witnesses, and other institutes set comparable requirements of objectivity and disclosure. Where the two conflict, the duty to the tribunal comes first.

The practical consequence is a different relationship with the client team. You can be asked to explain your evidence, to consider material you had not seen, and to reconsider a conclusion. You cannot be told what the conclusion is. A witness who accepts an instruction to reach a stated conclusion has stopped being an expert, and cross-examination usually finds it.

Proof of evidence structure and content

A proof is an evidential document, not an advocacy one, and it reads better when it is dull.

The structure that works is consistent across disciplines: qualifications and experience with the witness's relevant background stated plainly, a declaration of independence and the basis of the fee, the scope of the evidence and the matters not covered, the factual background and any agreed facts, the policy framework relevant to the discipline, the analysis with the method and inputs set out, the response to the authority's reasons for refusal, and a conclusion that answers only the questions within the witness's expertise.

Two mechanical points. The inquiry procedure rules require proofs to be submitted by a set deadline before the inquiry, normally four weeks, and a summary is required where a proof exceeds 1,500 words. Write the summary yourself rather than letting someone extract it, because the summary is what is read aloud and what the inspector may rely on most.

Appendices carry the technical material: survey data, model outputs, calculations, drawings and correspondence. Cross-reference them precisely. An appendix nobody can find in the middle of cross-examination helps nobody.

Say what you have not done. A daylight witness who has modelled the proposal but not the alternative should say so in the scope section rather than having it drawn out under questioning.

Statements of common ground and what they settle

A statement of common ground records what the parties agree, and its value is that it removes uncontested material from the inquiry timetable.

Agree the facts, the baseline data, the method where it is not in dispute, the policy text, the planning history and the site description. Do not agree matters of judgement to save time. And make sure the statement distinguishes clearly between agreed facts and agreed methodology on the one hand, and matters still in dispute on the other, because an ambiguous statement produces an argument about what was agreed.

Where two technical witnesses in the same discipline can narrow the gap, a joint statement listing agreed inputs and the specific points of difference is the most useful document either of them will produce. It also focuses cross-examination on the real question, which usually helps the better-prepared witness.

Watch the drafting. A sentence agreeing that a method is appropriate is not a sentence agreeing that the output is correct, and the difference matters when the other side quotes it back.

Cross examination and the limits of your expertise

Cross-examination tests three things: whether the witness understands their own evidence, whether the method is sound, and whether the witness will defend a position beyond what the evidence supports.

Four habits carry a witness through. Answer the question asked rather than the one you prepared for. Say you do not know when you do not know, since a guess that turns out to be wrong contaminates everything else. Stay inside your discipline, because an acoustician asked about heritage harm should decline the question and say why. And keep your file organised so that you can find the number you are being asked about.

Preparation is mostly re-reading your own material. Know every figure in your proof, where it came from, and what it would become if a challenged assumption changed. An advocate who finds a number you cannot source will return to it repeatedly.

An illustrative example. A transport witness is asked whether the trip rates would change if two of the seven survey sites were excluded as unrepresentative. The witness who has run that sensitivity in advance answers in one sentence. The witness who has not spends ten minutes losing credibility. The scenario is illustrative and the lesson applies to every discipline.

Where a witness must concede a point

Concession is part of the job and it is not a failure.

Concede where the evidence does not support the position, where an assumption has been shown to be wrong, where the other side's method is better for the specific question, and where a factual error has been identified. Do it clearly and immediately, then explain what the concession does and does not do to your overall conclusion, since a single input rarely changes the whole answer.

What damages a case is the witness who defends an untenable point for an hour and then concedes it, because the inspector reads that as a witness whose judgement is governed by the client's interest. Practitioners who have sat through it rarely forget the moment the inspector stops taking notes.

The same discipline applies to the material behind the evidence. Where a survey is out of date, say so, along the lines of the ordinary approach to checking whether a survey is still valid, rather than hoping nobody asks.

Costs risk from unreasonable evidence

Costs can be awarded in appeal proceedings where a party has behaved unreasonably and put another party to unnecessary expense. Evidence contributes to that in specific ways.

1. Pursuing a ground of appeal or a reason for refusal that the evidence cannot support.
2. Introducing new material late, so that the other side has to respond at short notice.
3. Failing to produce evidence the party said it would produce.
4. Relying on evidence whose method is shown to be flawed at its foundation.
5. Withdrawing a case or a substantial part of it at or shortly before the inquiry.

Witnesses rarely cause a costs award on their own. They do contribute to one, and a witness who tells the client early that a position cannot be evidenced is doing the most valuable part of the job. Where the discipline is one with published standards on independence and reporting, such as viability work assessed against RICS standards, a departure from those standards is an obvious line of attack.

Preparing a witness who has not appeared before

First-time witnesses need three things, and none of them is public speaking training.

They need to know the procedure: who sits where, that they will be sworn or affirm, that the advocate takes them through the summary, that cross-examination follows, then re-examination and the inspector's own questions, and that they may be recalled. They need a practice session on their own evidence with someone playing the other side properly, including the questions the client would rather nobody asked. And they need permission, given explicitly by whoever instructs them, to concede a point and to say they do not know.

Two further points are worth making to a new witness. The inspector's questions are usually the most important part of the session, because they show what is troubling the decision-maker. And the witness's job ends at the limits of their expertise, which is a relief rather than a restriction. Where competence itself is in issue, the meaning of competent person in planning legislation is worth understanding before the inquiry rather than during it.

One honest uncertainty. Inspectors vary in how much weight they place on oral evidence against the written proof, and some inquiries are effectively decided on the documents with cross-examination changing little. That is not a reason to prepare less, but it is a reason to write the proof as though it were the only thing anyone reads.

Reviewers who can sign off technical work are listed in the PlanScope professional directory, and drafting support for the underlying documents sits alongside it.

This is general guidance, not legal advice. Check the position with your professional institute, your advocate or a qualified adviser before relying on it.

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