Japanese Knotweed and Property Sales: Legal Risks for Sellers
Since 30 March 2026, solicitors accredited under the Law Society's Conveyancing Quality Scheme have had to use the sixth edition of the TA6 Property Information Form on every new residential sale. Earlier versions have been withdrawn. The new form is shorter and plainer than the ill-fated fifth edition, and it gives sellers more scope to say "not known" where they honestly do not know.
Japanese knotweed survives the redesign and sits in the environmental section of the form. And for sellers, it remains one of the most reliable ways to find yourself being sued long after you have handed over the keys. The risk is not that you have knotweed. The risk is what you say about it.
What the law actually requires of you
There is a widespread belief that having Japanese knotweed on your land is illegal. It is not. You are under no legal obligation to remove it from your own garden, nor are you obliged to tell the world it is there.
There are, however, three real legal edges to be aware of. It is an offence under section 14 of the Wildlife and Countryside Act 1981 to plant knotweed or otherwise cause it to grow in the wild. Knotweed and any soil containing its roots are classed as controlled waste, so they cannot go in your “green” bin, on the compost heap, or in a skip; they have to go to a licensed facility. And local authorities can serve a community protection notice under the Anti-social Behaviour, Crime and Policing Act 2014 on an owner who does nothing while the plant spreads. The Government's guidance on preventing the spread of invasive non-native plants sets out what is expected of landowners.
None of that is what usually catches sellers out. What catches sellers out is the form.
The form, and what it now asks
The TA6 is the Law Society's standard form completed by the seller and passed to the buyer's solicitor. Using it is not a statutory requirement, but in practice it is used in almost every residential sale, and the buyer is entitled to rely on the answers.
In the sixth edition, the knotweed questions appear at 8.6 and 8.7. You are asked whether the property is affected, with the options "yes", "no", and "not known", and whether there has been a survey or a management plan in place. The Law Society's explanatory notes for the sixth edition are unusually frank about the difficulty: a property is generally treated as at risk if knotweed is growing on it or within three metres of the boundary. Even where nothing is visible above ground, dormant roots or rhizomes may still be in the soil. For that reason, the notes acknowledge that many sellers answer "not known".
That is a significant shift in tone, and a helpful one. But it does not rescue a seller who answers "no" when they should have known better.
Why "no" is the dangerous answer
In a 2023 county court case, a buyer paid £700,000 for a house in southwest London after the seller had ticked "no" to the knotweed question. Once he moved in and cleared the garden, the buyer found knotweed growing behind a bush near the shed.
The seller's defence was that he had genuinely believed the answer was true; the plant, he said, had been hidden. The judge did not accept it. Expert evidence showed the knotweed had at one point stood around two metres tall and had been treated with herbicide during his ownership. The judge concluded that he did not genuinely believe the property was unaffected when he sold it.
The seller was ordered to pay around £32,000 in damages, covering the reduction in the property's value and the cost of investigating and excavating the plant, plus the buyer's legal costs of up to £95,000, on top of his own. The total bill ran to roughly £200,000, on a claim worth a fraction of that.
The lesson is not "lie carefully". It is that "no" is a positive statement that there is no knotweed. If the answer turns out to be false and the buyer relied on it in proceeding with the purchase, the seller may face a claim in misrepresentation. Limitation periods can be complex: a six-year period will commonly apply. A treated infestation from four years ago is not ancient history. It is a fact you know, and the buyer does not.
"Not known" is legitimate, but it is not a hiding place
If you genuinely do not know, "not known" is the honest answer, and the form now invites it. It shifts the burden of investigation onto the buyer, usually by commissioning a specialist survey. What it cannot do is launder knowledge you already have. "Not known" from someone who has a treatment invoice in a drawer is not a neutral answer; it is misleading.
Two further points are easy to miss. Your answers must be kept up to date: if knotweed appears or you learn something new between completing the form and exchanging contracts, you must tell your solicitor, who will inform the buyer. And if you are selling as an executor or under a power of attorney, you remain responsible for the answers you give, even if you have never set foot in the garden.
Knotweed that crosses a boundary
Knotweed near a boundary raises a second, separate risk: a claim in nuisance by the neighbour it spreads to.
In Network Rail Infrastructure Ltd v Williams [2018] EWCA Civ 1514, the Court of Appeal confirmed that a neighbour does not have to wait for physical damage before suing. The encroachment of the roots alone can interfere with the use and enjoyment of the land, and that is enough. Liability arises once the landowner knows, or ought to know, of the risk and fails to do anything reasonable about it.
The position was then significantly narrowed by the Supreme Court in Davies v Bridgend County Borough Council [2024] UKSC 15, a Welsh case. Knotweed had spread from council land onto Mr Davies's garden years before he bought it, and years before the council was in breach of any duty. He claimed residual loss in value that persisted even after treatment. The Supreme Court held unanimously that he could not recover it: the loss had already occurred before the council's breach began, so the breach did not cause it. In other words, historic spread now gives defendants a strong causation argument.
For a seller, the practical message remains unchanged. If knotweed on your land is heading for next door, deal with it, and do not assume the neighbour's claim is hopeless simply because Davies went the council's way.
Mortgages and surveyors: the seven-metre rule is gone
Sellers often assume that knotweed renders a property unmortgageable. That is no longer the position, and repeating it can unnecessarily cost you a sale.
The RICS professional standard on Japanese knotweed and residential property, in force since March 2022, scrapped the old seven-metre rule and replaced it with four management categories, A to D, based on the actual impact of the infestation rather than on crude distance. Retention of mortgage funds is generally expected only in the more serious categories, where the plant is damaging a structure or restricting the use of the garden. Knotweed simply visible on neighbouring land, within three metres of your boundary, does not ordinarily trigger a retention at all, although individual lenders may apply their own requirements.
If knotweed turns up during a sale
Do not attack it with a spade and a bottle of weedkiller, and do not say nothing and hope.
Instruct a specialist survey by a contractor accredited by the Property Care Association or the Invasive Non-Native Specialists Association. If treatment is needed, get a written management plan with an insurance-backed guarantee, typically ten years and transferable to the buyer. That package, handed over with the TA6, can provide the reassurance a lender and buyer need to proceed. Expect a conversation about price, but a documented, guaranteed infestation is saleable. An undisclosed one is a lawsuit.
Where to go from here
The knotweed question on the TA6 looks like a tick box. It is, in fact, a statement you are personally liable for, and one a buyer can rely on for years afterwards. If knotweed is, or may be, present at a property you are selling, or if you are unsure how to answer questions 8.6 and 8.7 honestly, speak to your solicitor before the form is signed and returned. It is a far cheaper conversation than the one that follows a claim.