Japanese Knotweed (Fallopia Japonica) was originally introduced to the UK in the 1850s as an ornamental plant and animal feed, but it has spread rapidly and estimates now suggest at least one infestation in every 10km2. Knotweed can grow 3 – 4m in a 10 week growing season, and as little as 0.7 grams of rhizome can produce a new plant within only 10 days. The rhizomes can spread to a depth of 3 metres, and 7 metres horizontally. This strong growth and invasive root system can damage concrete foundations, buildings, roads, paving and retaining walls. For good reason, therefore, Knotweed is described by the Environment Agency as “indisputably the UK’s most aggressive, destructive and invasive plant”.
Under the Environmental Protection Act 1990, Knotweed is “controlled waste” and must be disposed of in accordance with the proper procedures, including the Environmental Protection (Duty of Care) Regulations 1991. Further, as treatment of Knotweed involves the application of herbicides, the Control of Substances Hazardous to Health Regulations 2002 must be followed. In some cases, such as when chemicals are used in or near a watercourse, the Environment Agency must be informed (The Food and Environment Protection Act 1985 and The Control of Pesticides Regulations 1986). Although it is controlled waste, Japanese Knotweed is not a notifiable weed. Nevertheless whilst it is not an offence to have Knotweed on your land, under the Wildlife and Countryside Act 1981 it is a criminal offence, with a potentially unlimited fine and/or up to 2 years imprisonment, to plant Knotweed or otherwise cause it to grow in the wild. In the case of corporate bodies, such penalties can be imposed on an officer of the company if the offence was committed with that person’s consent or neglect. It is a defence to a prosecution to prove that all reasonable steps were taken and all due diligence was exercised.
Dealing with Knotweed may involve digging it up and burying it on or off site, treatment with a herbicide, or a combination of such measures. If it is to be removed, as it is classified as "controlled waste" all parts of the Knotweed and any contaminated soil must be removed and disposed of by licensed waste control operators. Transportation of this material off-site can be very costly, and also risks spreading the Knotweed. Alternatively, control of Knotweed by treatment by chemical means relies on the death of the extensive rhizome system. This is also very costly and usually must be repeated and continued for several years before effective control is achieved.
Landowners have a duty not to do anything that would cause an encroachment or physical damage to their neighbour’s land, and this may include a positive duty to intervene where encroachment has occurred or is likely to occur. If a landowner allows Knotweed to spread from his property onto a neighbour’s, then the neighbour will likely be entitled to an injunction obliging the landowner to abate the nuisance. The landowner may be liable in nuisance for any damage caused by an encroachment, and this could be substantial if development is delayed or prevented. Ultimately, the cost of dealing with Japanese Knotweed may be high, but in view of the fact that its presence can damage or impede the sale of a property, or affect its value, it seems that treatment or removal by licensed contractors will likely be the only safe approach.
The problem of securing a mortgage on a property affected by Knotweed has increased in recent years. If there is evidence of Knotweed at a property, or there is a history of Knotweed in the local area, a specialist survey may be required. Some lenders will decline to make any loan on properties – whether for purchase or re-mortgage – where Knotweed is present. For some lenders, if the Knotweed is not within 7 – 9 meters of a building, they will lend, but may impose a condition that the Knotweed be dealt with professionally within a specific timescale. Lenders may also insist on a full or part retention of any loan.
As a result of the destructive nature of Knotweed, and the potentially huge cost of dealing with it – in time and money – its presence can damage a property owner’s interest, reducing a property’s value, or preventing a sale, and making it unmortgagable. Consequently it is perhaps not surprising that the presence of Knotweed can lead to litigation. What is surprising is the relative dearth of case-law relating specifically to Knotweed. In Flanagan v Wigan Metropolitan Borough Council (unreported 1995), a private landowner issued proceedings against the local Authority in respect of Knotweed which had invaded his garden from the Authority’s neighbouring land. The Authority was ordered to treat a one metre strip along the boundary between the properties for three years, and to install a reinforced concrete boundary. The Authority was also ordered to contribute towards the landowner’s costs. Courts treat Knotweed as a continuing nuisance and analogous to tree root damage, meaning that it is generally no defence that a landowner "came to the nuisance". Although the courts have tended to apply similar principles derived from tree root cases, however, it is likely that as awareness of Knotweed increases, if a large-scale case were to reach court in the future a more strict liability may be imposed.
As well as claims against a neighbour (in nuisance) and against a surveyor/valuer (in professional negligence/breach of contract), claims may be brought against a seller, in misrepresentation. The Law Society Property Information Form contains "instructions to the seller" that "If you do not know the answer to any question, you must say so. If you are unsure of the meaning of any questions or answers, you should ask your solicitor". The Form is important for both buyer and seller, because the seller’s replies are representations and buyers are informed that they "are entitled to rely on the replies given to enquiries by the seller". When the seller replies to questions in the Form, therefore, he should give careful consideration to the content of the answers.
Since March 2013 there has been a specific section dealing with Knotweed: the Form asks sellers, "is the property affected by Japanese Knotweed? – Yes / No / Not Known." Plainly, if a seller is aware that the property is affected, he must answer "yes". What if a seller is unsure though? If he answers "no", it is likely this would be considered a positive assertion that he had checked, and that the property is clear. Thus if the seller answers "no", based on the best of his knowledge, but it later transpires that Knotweed is present, the seller may be liable to the buyer for misrepresentation. The position would likely be similar even if the seller qualified his answer with a phrase such as "not so far as the seller is aware", as this may still be seen as a representation that the seller has taken reasonable steps to ascertain the correct reply. Thus it would seem that if the seller does not know whether or not the property is affected by Knotweed, he should answer "not known" rather than "no", but this non-committal response could well cause the buyer to become suspicious – has the seller checked? Is he hiding something?
An alternative approach, when the seller does not know for sure but has no reason to believe that the property is affected by Knotweed, would be to answer "no", but adding the caveat that "no warranty is given, and the buyer is recommended to obtain a suitable survey to answer this question". In any event, a buyer would always be best advised to commission a survey, and the Form makes clear that (at least in relation to the physical condition of the property) "the replies should not be treated as a substitute for undertaking a survey or making independent enquiries, which you are recommended to do".
Finally, if the seller subsequently becomes aware, before exchange of contracts, that his original reply was inaccurate, or the circumstances have changed so that the original reply is no longer accurate, he should inform the buyer. The Form clearly states that if the seller later becomes "aware of any information which would alter any replies you have given, you must inform your solicitor immediately. This is as important as giving the right answers in the first place". If the seller does not do so, he could be liable for misrepresentation.