Alix Lee explains why buyers, sellers and experts should make themselves aware of the extent of the risks posed by the invasive weed, and the steps they can take to protect themselves.
What do Thierry Henry, the site of the London Olympic Stadium and a furniture designer all have in common? The answer, they have all faced the “threat” of Japanese knotweed on or near their land.
Remarkably, in the space of just weeks, we have seen two high profile cases addressing the knotty issue of Reynoutria japonica – Japanese knotweed. The cases have caused practitioner and experts alike to consider more closely the impact of various forms of natural nuisances on land and property transactions.
Downing v Henderson (unreported, 2023) and Davies v Bridgend County Borough Council [2023] EWCA Civ 80; [2023] PLSCS 27 2023 provide a clear reminder to landowners to ensure that they are not doing anything on their land (or otherwise knowingly failing to take action) that would result in an encroachment or physical damage to neighbouring land – buildings or crops (Leakey v National Trust for Places of Historic Interest or Natural Beauty [1980] QB 485).
Prevention is better than cure. Landowners are expected to take all reasonable steps to eradicate a nuisance from their land and prevent its spread to neighbouring land. Failure to do so may result in being faced with liability for all foreseeable and consequential losses and damages that follow, including the cost of remedial works – which, in the case of invasive species, could be considerable.
Current thinking
Professional expertise on Japanese knotweed has moved on over the last decade, although perhaps the same cannot be said for general public perception. Back in 2012, Japanese knotweed was branded by sensationalist media headlines as a “pariah” and a “menace”. Much was made of claims that the weed may cost millions of pounds to eradicate over a period of many years, causing landowners to face civil or criminal liability should they fail to comply and leaving developer dreams for sites in tatters.
In March 2022, the RICS published its Japanese knotweed and residential property professional standard to assist members who encounter Japanese knotweed when undertaking surveys and valuations. Arguably, it provides a more balanced view on this particular invasive species. While the guidance continues to acknowledge that Japanese knotweed is a challenge, common public perception may well be out of all proportion with the reality of the risk the plant poses. According to the RICS, Japanese knotweed in fact rarely causes structural damage to substantial buildings such as dwellings – certainly, not to the same extent as trees or buddleia – yet the existence of a substantial tree is less likely to strike fear into the heart of any nervous purchaser in quite the same way.
Japanese knotweed has undoubtedly had a detrimental impact on the value and saleability of a property, in some cases far in excess of the physical damage caused by the plant, and can also create a lasting stigma for a property, long after the plant has been successfully treated and eradicated.
Media headlines following the decision in Davies arguably have done little to challenge this trend and may potentially lead to an increase in claims from affected landowners seeking damages for a loss in value to their property as a result of having been encroached by Japanese knotweed, even after treatment and eradication of the plant.
Davies is an interesting case which has examined more generally the applicability of damages for residual diminution in value and economic loss in nuisance claims. The case also served an important reminder that a defendant landowner will be liable for damages for diminution in value of their neighbour’s property, if they fail to treat knotweed once they have actual or constructive knowledge of its existence.
What should landowners be doing?
Although it is not a crime to have Japanese knotweed on your land, it is a criminal offence to knowingly plant the weed or allow it to spread to neighbouring land.
As with tree roots, bamboo, giant hogweed or other invasive species, and also banks of soil, landowners need to be regularly inspecting their land and be alert to all types of natural nuisance that may exist.
Landowners may need to implement a programme of tree pruning and maintenance to prevent movement, undermining and settlement of neighbouring properties caused by encroaching tree roots. Land banks may need to be monitored and stabilised to prevent slips and culverts and drains inspected and cleared to prevent flooding. Structural damage caused by encroaching tree roots is nothing new and, as we face more extremes in terms of climatic conditions, it is likely that movement, subsidence and settlement may become more prevalent and serious an issue to landowners and the property industry as a whole.
Landowner vendors will ordinarily be asked to complete the sellers’ property information form (TA6) and this must be completed truthfully and accurately.
Downing has again highlighted the key difference between a response of “no” and “not known”. In this case, the claimant successfully sued the defendant for significant damages for misrepresentation. The court held that the seller could not honestly answer “no” to the issue of whether the land in question had been affected by Japanese knotweed where the plant had previously been cut back and treated with herbicide.
“No” should only be selected as an answer in the TA6 where the seller is absolutely certain that there has been no existence of the plant on the land. In the case of any uncertainty, the response of “not known” should be selected.
What should buyers do?
Prospective purchasers and developers need to shoulder responsibility too and “upskill”. Careful examination of the land and its surrounding is key. Experts in knotweed and other invasive species should be instructed in the event of any uncertainty. Purchasers and their surveyors alike need to be able to identify potential sources of natural nuisance. Vigilance in investigations and investment in effective pro-active solutions where appropriate is key.
Additional precautionary surveys should be implemented and become standard practice for brownfield sites, roads, rivers and railway lines, where the risk of contamination by Japanese knotweed may be heightened from fly tipping.
What should the experts be doing?
The public perception of invasive non-natural species may well be creating a self-perpetuating issue which results in a continued blight to the land, resulting in a significant diminution in value, even where the infestation has been treated and eradicated.
A surveyor may be negligent in their duty to their client if they fail to report on the existence of Japanese knotweed and advise their client on the risk (see Ryb v Conway Chartered Surveyors (unreported, 2019)).
Any attempts to exclude liability or include complex disclaimers in terms of business with clients is likely to receive short shrift from the courts and fail to meet the requirements of the Consumer Rights Act 2015.
Lawyers have an important role to play as well. Their vendor clients need to understand the importance of their honest responses to the TA6. Similarly, prospective purchaser clients must properly investigate the land and instruct the right experts to undertake the correct and most relevant surveys and reports. Clients must be aware of the difference between a valuation and a survey report and the differing detail and depth of various surveys. Standard residential valuations and surveys are not specifically focused on finding and advising on Japanese knotweed, for example.
There is no obligation on a seller to complete a TA6 and, where this is refused, lawyers should be asking the appropriate direct questions of the vendor.
Lawyers also need to be advising their clients that some mortgage lenders may be reluctant to lend on properties where Japanese knotweed is present. Household insurance policies may also not cover the cost of damage caused by Japanese knotweed, bamboo and other non-native invasive species.
More generally, there needs to be a change in public understanding and perception of risk relating to Japanese knotweed and other natural nuisances. The RICS has identified that the roots of the mighty oak may be far more damaging to an adjoining dwelling than Japanese knotweed, and yet there remains a significant challenge for valuers who, despite the developing expertise, are pressured to follow the market trends rather than lead.
They will need to accurately establish the extent to which a purchaser – in full knowledge that a property is, or perhaps was previously, affected by Japanese knotweed – will seek to reduce their offer for the property compared with what they would have offered for the property had it not been affected.
Duty between neighbours
A lawful act on a person’s own land becomes an unlawful private nuisance when the consequences of that act:
- Causes an encroachment on neighbour’s land; or
- Causes physical damage to a neighbour’s land, or to buildings, works or vegetation on that land; or
- Unduly interferes with a neighbour’s comfortable and convenient enjoyment of their land.
In addition, an owner or an occupier of land continues to be a nuisance if, with actual or presumed knowledge of its existence, they fail to take reasonable steps to bring the act complained of to an end.
Alix Lee is a senior associate and professional support lawyer at Cripps
