Expert witness costs and proofs of evidence

Budget an expert witness at a planning appeal by topic rather than by sitting day, because the sitting days are the smallest part of the bill. A planning witness on a contested major appeal will spend most of the fee on drafting a proof, assembling appendices, negotiating a statement of common ground and preparing a rebuttal, all of which happen before anyone walks into the inquiry room. The expert witness cost on a planning appeal is therefore driven by how many topics are in dispute and how far apart the two sides are on each.

Narrow the topics and the budget falls. That is the only reliable lever available.

What a proof of evidence has to contain

A proof is the witness's evidence in chief, written, served in advance and adopted on oath or affirmation at the inquiry. Under the Town and Country Planning (Inquiries Procedure) (England) Rules 2000 it must be sent to the Planning Inspectorate not later than four weeks before the inquiry opens, and any proof longer than 1,500 words needs a summary served with it.

The content follows a settled shape: the witness's qualifications and experience, the scope of the evidence, the factual background, the policy framework, the assessment, the response to the reasons for refusal and to third party evidence, and a conclusion. Appendices carry the supporting material.

Two things make a proof expensive. The first is length, because every page has to be checked, cross-referenced and capable of being defended under cross-examination. The second is scope creep, where a planning witness ends up covering heritage, highways and drainage because nobody wanted to pay for three witnesses. That saving is usually false, since a witness giving evidence outside their field is the easiest target in the room.

Drafting, review and rebuttal rounds

The realistic drafting sequence runs to three or four rounds. A first draft from the witness, a review by counsel or the lead consultant, a revised draft against the other side's statement of case, and a final version once the statement of common ground is settled.

Rebuttal proofs are the variable nobody budgets for. Where the timetable allows them, a rebuttal has to be written quickly, after the other side's proofs land and usually within a fortnight, and that compressed work is charged at a higher effective rate because it displaces everything else in the witness's diary. On an appeal with four witnesses on each side, four rebuttals is a meaningful addition to the budget.

Ask for a fee structure that separates the main proof, the rebuttal and the attendance. A single lump sum covering all three tends to break down when the other side serves 300 pages of appendices a month before the inquiry.

Appendices and the evidence base

Appendices are where the real cost often sits, because they are new work rather than written argument.

A heritage witness may need a photographic survey from agreed viewpoints. A highways witness may need a fresh traffic count or a junction model rerun. A viability witness needs an appraisal and sensitivity runs, and the review mechanism that follows from it is covered in budgeting a viability appraisal and the review it triggers. A ground conditions witness may need further investigation, as discussed in budgeting ground investigation on a brownfield plot.

Decide early which appendices are being produced for the inquiry and which already exist from the application stage. Material prepared for the original submission can usually be appended as it stands. Material produced to answer a new point in the refusal reasons is new commissioned work with its own fee and its own lead time, and surveys with seasonal windows cannot be accelerated at any price.

Round table sessions and conferencing

Not every topic needs cross-examination. Inspectors increasingly deal with conditions, obligations and narrow technical disagreements in a round table session, where the parties and the inspector work through a list without formal examination.

Round tables cost the applicant less, because a witness attends for a defined session rather than waiting two days to be called. They also suit topics where the disagreement is about numbers rather than credibility. Ask for them at the case management conference, and say which topics you think suit the format.

Witness conferencing, where both sides' experts on the same topic give evidence together, is used less often in planning than in other jurisdictions. It can compress a day of cross-examination into a morning. It also exposes a weaker witness quickly, so it is a tactical choice rather than a saving.

Where a statement of common ground reduces cost

The statement of common ground is the most underused cost control in the inquiry process. It records the facts both sides accept, which means neither witness has to prove them.

Good ones cover the site description and planning history, the relevant policies and their status, agreed technical outputs such as trip rates or flood levels, the list of matters actually in dispute, and the conditions and obligation heads of terms if permission were granted. Every item agreed is a paragraph the witnesses do not have to write and a line of cross-examination that disappears.

Start it at the case management stage, not three weeks before the inquiry. And put a named person on each side in charge of it, because a statement of common ground negotiated by four witnesses in parallel takes longer than writing the proofs did.

Witness availability and the inquiry diary

Inquiry dates are fixed months ahead and specialists are booked months ahead, so availability shapes the budget in ways that have nothing to do with the merits.

Three practical points. Confirm each witness's availability for the full sitting window before the date is agreed, including the contingency days. Check whether a witness has a competing inquiry in the same period, because a clash discovered late means either a substitute witness reading someone else's proof or an application to move the dates. And expect waiting time to be charged, because a witness who attends on day two and gives evidence on day four is working throughout.

For an appeal that was itself triggered by a screening or scoping dispute, the evidence base may already be partly built, and the costs of that earlier stage are set out in EIA screening and scoping request costs.

Budgeting per topic rather than per day

Build the budget as a matrix of topics against stages. For each disputed topic, price the proof, the appendices, the statement of common ground input, the rebuttal, the attendance and the post-inquiry work. Then total it.

That structure does two useful things. It shows immediately which topic is consuming the budget, which focuses the question of whether to concede it. And it gives you a defensible figure to take to a board, rather than a daily rate multiplied by an optimistic number of days.

As an illustrative example, an appeal with housing land supply, heritage and highways in dispute needs three witnesses, three proofs, three rebuttals and three sets of appendices, plus a planning witness to pull the balance together. Concede highways on the basis of an agreed mitigation package and the budget loses a witness, a rebuttal, a traffic survey and a day of sitting time. That is the calculation worth doing before the statement of case is served, and the equivalent discipline for fixed-fee work on the application side is set out in what a planning agent's fixed fee includes.

Costs awards are the other side of the budget. The Planning Practice Guidance on appeals allows an award against either party for unreasonable behaviour, and withdrawing a topic the week before the inquiry after the other side has prepared evidence on it is one of the recognised grounds.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. If you want to compare the cost of drafting the underlying reports, see PlanScope pricing.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.