What Should a Conveyancer Tell a Buyer About Japanese Knotweed?

If Japanese knotweed is found on a property or neighbouring land, what should the buyer’s conveyancer actually explain before exchange?

It is not enough simply to repeat the seller’s answer or mention that knotweed may be present. The buyer needs to understand what has been identified, what remains uncertain, whether further investigation is required and how the problem could affect treatment, mortgageability and a future sale.

Lexsure’s Report on Title resource, Japanese Knotweed, including the implications of the Network Rail case, provides wording for conveyancers to consider when explaining these issues to a purchaser.

Why does Japanese knotweed need to be explained before exchange?

A Report on Title should help the client make an informed decision before becoming legally committed. Repeating an answer from the seller’s property information form without explaining its significance may not achieve that purpose.

Where Japanese knotweed is known or suspected, the report may need to address:

• where the growth has been identified;
• whether it is within the property or on neighbouring land;
• the source and reliability of the information;
• whether a surveyor or specialist has inspected it;
• whether a management or treatment plan exists;
• whether any treatment plan is supported by an insurance backed guarantee;
• what the proposed mortgage lender requires;
• the possibility of spread from adjoining land;
• future sale and remortgage implications; and
• the potential for disputes with neighbouring owners.

The precise advice will depend on the evidence available in the transaction. A standard paragraph cannot decide whether knotweed is present, assess the severity of an infestation or replace specialist advice. Its purpose is to ensure that the legal and practical implications are not left unexplained.

What did the Network Rail Japanese knotweed case decide?

In Network Rail Infrastructure Ltd v Williams and Waistell [2018] EWCA Civ 1514, Japanese knotweed had grown on railway land adjoining two residential properties.

The homeowners argued that knotweed rhizomes had encroached onto their land and that Network Rail had failed to take reasonable steps to control the problem after becoming aware of it.

The Court of Appeal treated the physical encroachment of Japanese knotweed rhizomes as capable of amounting to an actionable nuisance. The significance of the problem was not confined to visible structural damage. The presence of knotweed could interfere with an owner’s use and enjoyment of the property by imposing an immediate burden and creating a risk of further spread.

The decision helped move the legal discussion beyond the simple question of whether knotweed had already damaged a building. Location, encroachment, knowledge and the steps taken to control the plant could all be relevant.

Does knotweed automatically entitle an owner to compensation?

No. The presence of Japanese knotweed does not automatically create a right to recover compensation for a reduction in property value.

The Lexsure resource displays a change date of 9 January 2019 and explains that its advice was updated following the Network Rail decision. Any precedent based on a historical case development should still be reviewed against subsequent authority before use.

In Davies v Bridgend County Borough Council [2024] UKSC 15, the Supreme Court considered a claim for residual diminution in value after Japanese knotweed had spread from neighbouring land.

The claim failed because the relevant encroachment had occurred before the defendant’s actionable breach of duty. The necessary causal connection between the later breach and the claimed loss had not been established.

The decisions should not therefore be reduced to a statement that knotweed near a property automatically entitles the owner to compensation. The facts, timing of the encroachment, knowledge of the landowner, reasonable response and causation remain important.

For conveyancers, this reinforces the importance of describing the actual risk rather than predicting the outcome of a hypothetical future claim.

Can a conveyancer rely on the seller’s answer?

The seller’s response concerning Japanese knotweed is an important starting point, but it is not necessarily the end of the investigation.

A negative answer may be qualified by the wording of the particular property information form and by the extent of the seller’s knowledge. It does not amount to a specialist survey or an absolute guarantee that knotweed is absent.

If a survey, valuation, environmental report or other evidence raises a concern, the conveyancer should not assume that the seller’s answer resolves the inconsistency. Further enquiries or specialist investigation may be appropriate.

The Report on Title should distinguish clearly between:

• what the seller has stated;
• what a surveyor or specialist has observed;
• what remains unconfirmed; and
• what the buyer should do before exchange.

What if the knotweed is on neighbouring land?

A buyer may assume that Japanese knotweed is irrelevant if it is outside the property’s legal boundary. The Network Rail litigation demonstrates why that assumption can be unsafe.

Growth on adjoining land raises questions about proximity, spread, access, responsibility and the willingness of the neighbouring owner to implement an effective treatment programme.

A treatment plan confined to the property being purchased may provide incomplete protection if the source remains untreated next door. The buyer may need specialist advice about the likelihood of spread and the proposed management arrangements.

The conveyancer can then consider the legal documentation, the lender’s requirements and any further enquiries or undertakings needed before exchange.

Can Japanese knotweed affect the buyer’s mortgage?

Japanese knotweed can affect valuation and mortgageability. A lender may require further evidence about the location and extent of the growth, the proposed treatment and the protection available to future owners.

Depending on the circumstances and the lender’s requirements, this may include:

• a specialist inspection;
• a management or treatment plan;
• evidence that treatment has already started;
• an insurance backed guarantee;
• confirmation that the guarantee can be transferred; or
• a specific report to the lender.

Different lenders may take different approaches. Their instructions can also change over time.

Our earlier article asked whether lenders were placing increasingly complicated knotweed obligations on conveyancers. That article records the position discussed in 2016 and should not be used as current lender guidance. Its continuing relevance lies in demonstrating that lender requirements have not always been uniform.

Does a mortgage offer mean the property will be easy to sell?

A mortgage offer does not necessarily establish that Japanese knotweed has been considered or that the property will be readily acceptable to the wider lending market.

A particular lender may be willing to proceed because specified evidence or treatment arrangements are in place. A future purchaser using another lender may encounter different requirements.

This is where mortgageability and marketability overlap. The question for the buyer is not confined to whether the present lender will release the mortgage advance. The buyer should also understand whether the issue could reduce the pool of future purchasers, delay a later transaction or require further expenditure before resale.

Our article on why Japanese knotweed can cause buyers to reconsider a purchase examines the practical effect that the issue can have on buyer confidence.

What should the buyer understand before proceeding?

Depending on the circumstances, the Report on Title should enable the buyer to understand:

• whether Japanese knotweed has been confirmed or is merely suspected;
• whether it is situated within the property or on adjoining land;
• whether a specialist assessment has been obtained;
• the proposed treatment and monitoring arrangements;
• the duration and transferability of any guarantee;
• whether the lender has been informed where required;
• the likely effect on future buyers and mortgage lenders;
• the risk of spread or recurrence; and
• the limitations of the information currently available.

The buyer should also understand that legal advice is not a substitute for horticultural, structural or valuation advice. Where those disciplines overlap, the report should identify which questions require another professional’s expertise.

What if the problem only emerges after purchase?

A homeowner may discover Japanese knotweed years later when a surveyor identifies it during a sale or remortgage.

That does not automatically establish that the problem existed at the time of purchase or that the original conveyancer was at fault. Knotweed may have spread or become established after completion.

It can nevertheless justify examining the historical record. Relevant documents may include:

• the seller’s property information form;
• the survey and mortgage valuation;
• pre contract enquiries and replies;
• specialist reports or treatment documents;
• the original lender’s instructions;
• the Report on Title; and
• the advice provided before exchange.

When I Bought’s Japanese knotweed guide is intended for owners who first encounter the issue when selling or remortgaging and want to understand what may have been known, investigated or explained when they purchased the property.

Should historical lender instructions be checked?

If the problem concerns an earlier mortgaged purchase, the lender’s current requirements cannot establish what the conveyancer was instructed to do at the time.

The relevant lender and transaction date both matter. An investigation may need to consider the requirements applying when the issue was identified, when the Certificate of Title was submitted and when the transaction completed.

Our guide to historical mortgage lender requirements concerning Japanese knotweed explains why a present day handbook should not be substituted for the wording applying during the original transaction.

The historical instructions form only one part of the evidence. What the conveyancer was required to tell the lender and what the purchaser should have been told are related but separate questions.

A warning should lead to an informed decision

A useful Report on Title does more than insert the words “Japanese knotweed”. It should connect the available evidence with the consequences that matter to the buyer.

The Lexsure Japanese knotweed Report on Title resource provides wording for conveyancers to consider. Because the page records an update made in 2019, firms should ensure that any wording used is reviewed alongside current law, current lender instructions and the particular facts of the transaction.

The objective is not to frighten every purchaser away from a property where knotweed has been identified. It is to ensure that the purchaser understands the investigation, treatment, mortgage and resale implications before deciding whether to proceed.

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This article provides general information and is not legal, valuation, surveying or horticultural advice. Japanese knotweed cases depend on their particular facts. The applicable law, professional standards and mortgage lender requirements should be checked at the time of the transaction.