At SE Knotweed, an expert witness report is an independent, CPR Part 35 compliant assessment of a Japanese knotweed case, written for a court to record the source, extent and remediation cost in a private nuisance claim.
An expert witness report costs from around £750 to £2,500 depending on the site, the survey work needed and whether a joint statement or attendance at court follows, and we confirm the fee on instruction.
A Japanese knotweed expert witness report is an independent, written assessment of a knotweed case, prepared to Civil Procedure Rules Part 35 for use in a private nuisance or diminution claim. At SE Knotweed we confirm the species, map the stand against the boundary, identify the likely source and route of spread, and set out the remediation and its cost, with the expert's overriding duty stated as being to the court rather than to the instructing party.
It differs from an ordinary survey because it must be balanced, disclose the facts against as well as for the client, and carry a statement of truth and a declaration of the expert's duty. If you have a letter of claim or a defence to answer, contact us about an expert report.
You need an expert witness report when a knotweed dispute is heading to court or to formal pre-action correspondence, most often a private nuisance claim over encroachment from adjoining land, a boundary dispute, or a misrepresentation claim after a sale. The report gives the tribunal the technical findings a solicitor cannot give: whether the plant is knotweed, where it came from, how far the rhizome extends and what remediation costs.
It also supports a defence, where an owner is accused of allowing spread and needs the true extent and history recorded. Claims turn on breach of a duty and on the facts, so the report sits alongside the legal position and the valuation evidence rather than replacing them.
An expert witness report costs from around £750 to £2,500, driven by the size of the site, the survey and any excavation trial pits needed to confirm rhizome extent, and whether the instruction runs on to a joint statement and attendance at court. A single-stand residential boundary case sits at the lower end, a multi-stand commercial site at the higher end.
We quote the report fee and any court attendance separately at instruction, so the figures are indicative until we have seen the pleadings and the site. A survey is usually the first stage, and its findings feed the report.
The report contains the expert's qualifications and CSJK status, the instructions, a description of the site and the inspection, the confirmed identification, a measured plan of each stand and the 3 metre zone, the likely source and mechanism of spread, the recommended remediation with an indicative cost, and the RICS 2022 management category from A to D.
It closes with the CPR Part 35 statements: the substance of the facts and instructions, the range of opinion where one exists, a statement of truth, and the declaration that the expert understands the duty to the court. We write it so a solicitor, a judge and the other side's expert can each follow the reasoning.
We assess the source and extent by inspecting both sides of the boundary where access allows, recording the age and density of the stands, the direction of rhizome growth, and any cut, tipped or disturbed ground that points to how the plant arrived. Where the extent below ground is disputed, hand-dug trial pits or, on larger sites, detection dogs confirm how far the rhizome runs.
The mechanism matters because knotweed spreads from rhizome and stem fragments in soil and water, not from seed in the UK, so the report can often distinguish natural encroachment from material moved by works. That evidence is what a nuisance claim relies on, and the way it spreads shapes the finding.
The report supports a claim by proving the technical elements a nuisance action needs: that the plant is Japanese knotweed, that it encroached from the defendant's land, and what it costs to remediate and monitor. Those findings feed the legal test of whether the defendant knew or ought to have known and failed to act reasonably.
On value, we record the RICS category and the remediation cost, but a residual fall in market value is a valuation matter, and in Davies v Bridgend [2024] UKSC 15 the Supreme Court held that residual diminution is not recoverable where the spread happened before the defendant was in breach. We state that limit plainly rather than promising a payout.
A CSJK-qualified expert gives the court a witness whose identification and assessment method follow the recognised surveying standard for Japanese knotweed, which is what makes the findings hard to challenge on the technical side. We hold the CSJK qualification, PCA approval and TrustMark registration (licence 2902558), and we prepare the report to CPR Part 35.
That combination matters because a report is only as strong as the expertise behind it and the independence on its face. We give evidence on the plant, its spread and its remediation, and leave valuation to a RICS valuer, so each part of the case is covered by the right discipline.
Tell us the address and what a surveyor flagged. We confirm the plant, record the RICS category and set out the figures.