No Japanese Knotweed, Said the Seller. The Garden Told a Different Story

A buyer completes the purchase of a £700,000 home after the seller states that the property is not affected by Japanese knotweed. The buyer later discovers the plant in the garden. Evidence suggests that it had previously grown to a substantial height and had been treated with herbicide. The seller’s answer becomes the focus of an expensive misrepresentation claim.

The reported County Court decision in Downing v Henderson provides a stark warning about the Japanese knotweed question in the Property Information Form. It also raises the characteristic When I Bought question: if knotweed is discovered after completion, what was known, disclosed, inspected and explained when the property was purchased?

The seller answered no

The buyer, Mr Downing, purchased the property from Mr Henderson in 2018 for approximately £700,000.

As part of the conveyancing process, the seller completed the Property Information Form. The form contained a specific question about whether the property was affected by Japanese knotweed. The seller reportedly answered “No”.

After completion, the buyer discovered Japanese knotweed in the garden. The seller maintained that he had lived at the property for around three years and had not known that the plant was present.

The difficulty for the seller was the physical and expert evidence. Published accounts of the decision state that the knotweed had previously reached approximately two metres in height and had been treated with herbicide.

The court was reportedly not persuaded that the negative answer was reasonably given.

The financial consequences extended beyond removing the plant

The seller was reportedly ordered to pay approximately £32,000 in damages. That figure included the cost of investigating and excavating the knotweed together with diminution in the property’s value.

Published legal commentary also records an order requiring the seller to pay approximately £95,000 towards the buyer’s legal costs. Press accounts suggested that the seller’s overall exposure, once his own costs were included, may have been considerably higher.

The case demonstrates why the cost of a knotweed dispute cannot be measured solely by obtaining a quotation for treatment. The consequences may include:

• specialist inspection and identification costs;
• excavation or a multi-year treatment programme;
• professional fees;
• legal costs;
• reduced property value;
• mortgage lender restrictions;
• difficulty selling or remortgaging; and
• a possible misrepresentation claim against the seller.

A comparatively inexpensive attempt to cut back or suppress visible growth can therefore create a much larger problem if it is followed by an inaccurate answer during the sale.

What does the seller’s answer actually represent?

The Property Information Form does not require a seller to provide a scientific guarantee that no knotweed rhizome exists anywhere beneath the land. However, a seller must answer the question honestly and with appropriate care.

A seller should not answer “No” merely because:

• no stems are visible on the day the form is completed;
• the plant was cut down during the previous season;
• herbicide has temporarily suppressed its growth;
• the garden has been covered with decking, paving or artificial grass;
• the seller does not know the name of the plant; or
• the problem is believed to originate on neighbouring land.

Earlier treatment records, invoices, guarantees, photographs and communications with neighbours or contractors may all be relevant to what the seller knew.

If the seller is genuinely unable to answer, that uncertainty should be dealt with accurately. “Not known” is not a convenient alternative where the seller has information pointing to the presence or treatment of knotweed.

Why treatment does not remove the disclosure question

Japanese knotweed may be controlled through a professional treatment programme, but the existence of a treatment plan does not turn a previous infestation into a non-event.

A prospective buyer may need to know:

• when the knotweed was first identified;
• where it was located;
• whether it originated within the property or on adjoining land;
• what treatment has been undertaken;
• whether excavation has occurred;
• whether viable rhizomes may remain;
• the duration of the management plan;
• whether the guarantee is insurance backed;
• whether the benefit can pass to a buyer and lender; and
• what monitoring or access obligations will continue after completion.

The correct answer is not necessarily to reject every property that has experienced Japanese knotweed. The buyer needs an accurate history and sufficient evidence to understand what remains to be managed.

Could the surveyor also be responsible?

The seller’s disclosure is only one part of the transaction. A buyer may also have commissioned a valuation, home survey or more detailed building survey.

Whether a surveyor should have identified knotweed will depend on the scope of the inspection, the season, accessibility, visible growth and evidence of previous treatment or concealment.

A survey is not necessarily defective merely because knotweed is discovered later. It may have been dormant, recently cut down, concealed by garden structures or situated beyond the inspected land.

Conversely, visible mature growth or obvious signs of treatment may require investigation and appropriate reporting. The buyer’s claim against the seller and any claim against a surveyor involve different duties and should not be treated as interchangeable.

What should the conveyancer do with the answer?

A conveyancer does not normally inspect or identify garden plants. The conveyancer’s task is to review the seller’s replies, search results, survey information and mortgage lender instructions and then advise the buyer on their combined significance.

If the seller answers “Yes”, the conveyancer may need to obtain:

• the specialist survey or identification report;
• the treatment or management plan;
• the contractor’s qualifications and membership details;
• the insurance-backed guarantee;
• evidence that the documents are transferable;
• a plan showing the location and extent of the infestation;
• information about neighbouring land; and
• the proposed mortgage lender’s requirements.

If the seller answers “No” but the buyer’s survey refers to suspected knotweed, the inconsistency should be resolved before exchange. The negative answer should not simply be repeated in the Report on Title as if it displaced the surveyor’s concern.

Likewise, if the seller supplies evidence of previous herbicide treatment but maintains that the property has never been affected, further enquiries are plainly required.

Why the mortgage lender’s requirements matter

Mortgage lenders do not necessarily take an identical approach to Japanese knotweed. Requirements may address matters such as distance from the property, the location of the infestation, damage, professional treatment plans and insurance-backed guarantees.

The conveyancer must consider the lender’s applicable instructions and report the matter where required. The fact that one lender accepts a property does not establish that the wider mortgage market will take the same view.

This is important for the buyer as well as the lender. A property that can be mortgaged today may still face a reduced pool of lenders and buyers when it is sold again.

Our earlier article, Japanese Knotweed: Knot Disclosing to Lenders, recorded how different lenders were already developing more detailed reporting requirements. It remains a useful historical illustration, but should not be treated as a statement of the requirements applying today.

What if the knotweed is discovered years after completion?

The buyer should first establish that the plant has been correctly identified. A qualified specialist may need to inspect the property, map the affected area and assess whether the growth originated on the property or spread from neighbouring land.

The buyer should then obtain the original purchase documents, including:

• the Property Information Form;
• the contract enquiries and replies;
• the mortgage valuation;
• any private survey;
• the conveyancer’s Report on Title;
• photographs and marketing particulars;
• treatment records supplied by the seller;
• communications concerning the garden or adjoining land;
• the mortgage offer and special conditions; and
• the lender requirements applying when the purchase completed.

The investigation should consider several distinct questions:

1. Was knotweed present when the property was sold?
2. What did the seller know or have reasonable grounds to know?
3. Was the Property Information Form answer accurate?
4. Should the surveyor have identified visible evidence?
5. What did the buyer’s conveyancer receive and report?
6. What did the original mortgage lender require?
7. What loss has the buyer actually suffered?

The final question is important. Treatment cost, investigation cost, diminution in value and the consequences of a failed sale must be evidenced rather than assumed.

What did the original lender require?

If the buyer’s present difficulty concerns a sale, remortgage or allegation that the matter should have been reported originally, today’s UK Finance Mortgage Lenders’ Handbook cannot establish what applied years ago.

Lenders have changed their Japanese knotweed requirements over time. The relevant historic record may show whether the lender required notification, a treatment plan, a guarantee, specialist evidence or another response on the transaction date.

The Lexsure Lender Archive Japanese knotweed records allow the original lender and date to be selected. This can help establish the lender wording recorded at the time.

The historic lender requirement is evidence of the instruction framework. It does not establish whether the seller misrepresented the position, whether the surveyor was negligent or whether the conveyancer breached a duty. Those questions require the complete file and the facts of the individual transaction.

The Report on Title should explain the practical consequences

A Report on Title should do more than tell the buyer that Japanese knotweed exists or that a management plan has been supplied. It should explain what the documents mean for ownership, occupation, the mortgage and a future sale.

Relevant reporting may include the likely duration of treatment, continuing monitoring obligations, the status of the guarantee, the possibility of regrowth, neighbouring land and the lender’s position.

Lexsure’s Japanese knotweed Report on Title wording provides an example of a precedent designed to explain the issue and the implications of the relevant case law to the buyer.

A short answer can carry a long liability

Downing v Henderson demonstrates the danger of treating the knotweed question as a routine box-ticking exercise.

A seller who knows about previous growth or treatment should not assume that cutting the plant down permits a negative answer. A buyer should not assume that “No” is a guarantee backed by inspection. A conveyancer should not ignore inconsistencies between the form, survey and other documents.

If knotweed emerges after completion, the real investigation begins with the records from the purchase. What was growing? What had been treated? What did the seller say? What did the surveyor see? What did the lender require? And what advice did the buyer receive before becoming legally committed?

This article is for general information only and is not legal, valuation, horticultural or environmental advice. The account of Downing v Henderson is based on published reports of an unreported County Court decision. Any potential claim or defence should be considered by reference to the court record, expert evidence and the facts of the individual transaction.