This article is co-authored by Chong Goh, Paralegal, Real Estate Disputes
What is Japanese Knotweed?
Japanese Knotweed is a highly invasive plant species which must be controlled. Knotweed is estimated to affect around 5 per cent of UK homes, and property owners can be liable if it is allowed to spread into the wild or onto the property of others.
The process for treating the plant usually takes over three years and, if found on a property, may cause a decrease in value, even once treated.
Recent Court of Appeal judgement on Japanese Knotweed liability
The case of Davies v Bridgend County Borough Council  EWCA Civ 80, recently held Bridgend County Borough Council liable for damages for Japanese Knotweed encroaching onto the Claimant’s land, even though there was evidence of the invasive plant encroaching on the Claimant’s land prior to his purchase.
The decision of the Court of Appeal awarded the Claimant damages of £4,900. The decision and potential liability for Japanese Knotweed encroaching onto another’s land will likely worry property owners dealing with this persistent nuisance.
Since 2004, Mr Davies (the “Claimant”) has owned a property in Bridgend, Wales, which is adjacent to land owned by Bridgend County Borough Council (the “Council”). Prior to Mr Davies purchasing his property, Japanese Knotweed had been growing unnoticed on the adjoining property owned by the Council and rhizomes, a horizontal underground plant stem which can produce the shoot and root systems of a new plant, had spread underground to what is now the Claimant’s land.
Timeline of the case
The Claimant became aware of the issue of Japanese Knotweed encroaching onto his land in 2017. The Council had been aware of the plant on their land since 2013, however, it only started treating the problem in 2018. The Claimant submitted a Letter of Claim in 2019.
The claim was first heard by District Judge Fouracre in Swansea County Court in 2021. The Claimant claimed £4,900 for the residual diminution in value to his property, from the stigma or blight of having previously had Japanese Knotweed on the Claimant’s property. Using Williams & Waistell v Network Rail Infrastructure Limited  QB 601 as a precedent, DJ Fouracre concluded the Claimant’s damages were irrecoverable, as the residual diminution was regarded as pure economic loss. In the judgment, applying Williams & Waistell v Network Rail Infrastructure Limited  it was said, “the purpose of the tort of nuisance is not to protect the value of property as an investment or a financial asset”. However, it was acknowledged the Council had breached its duty of care to the Claimant by failing to treat the Japanese Knotweed from 2013 to 2018, and the damage leading to the loss was caused by the nuisance of the Japanese Knotweed.
The Claimant appealed to Circuit Judge HHJ Beard in 2022. The appeal was dismissed, with HHJ Beard agreeing with CJ Fouracre’s judgment and assessment of the claim.
2023 Court of Appeal decision
In 2023, Lord Justice Baker, Lord Justice Briss and Lord Justice Snowden, sitting in the Court of Appeal, overturned both previous judgments disagreeing with the interpretation of Williams & Waistell v Network Rail Infrastructure Limited , commenting that it was originally misused and there is no authority for economic loss that was caused by a nuisance due to a breach by the defendant.
While the Council tried to argue the loss to the Claimant’s property would have occurred whether they had treated the Japanese Knotweed in 2013 or 2018, it was dismissed by the Court of Appeal citing Delaware Mansions  1 AC 321. LJ Briss stated, “the fact the encroachment was historic was no answer when there was a continuing breach of duty as a result of persisting encroachment”.
The Court of Appeal awarded the Claimant £4,900 in damages for the residual diminution of his property, due to the stigma of Japanese Knotweed.
However, the Supreme Court has granted permission to appeal for this case, which could turn the tables once again.
The problem of Japanese Knotweed for property owners
The nuisance of Japanese Knotweed is one that, unfortunately, is not going away. With the long treatment time and highly invasive nature of the plant, it is important for property owners to understand their potential liability for the spread of Japanese Knotweed and how to mitigate the problems it can cause.
The purchase of insurance prior to any Japanese Knotweed issues and immediate treatment of the Japanese Knotweed can help to mitigate the problem. However, each case will be different and the set of circumstances of each claimant and defendant may result in different outcomes.
The Hamlins Real Estate Disputes team has expertise in both commercial and residential matters. We seek to obtain the best outcome possible for every client, no matter how big or small the issue may be.
If you have a problem with Japanese Knotweed encroaching onto your property, or Japanese Knotweed on your property has spread to neighbouring land or to another property, please contact a member of our Real Estate Disputes team who can advise you on the best approach.