1st July 2024

Japanese knotweed: Notable decision by The Supreme Court

By Kate Andrews & Chong Goh

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 Japanese knotweed is found on a property, it may cause a decrease in value, even once treated.

A notable decision by The Supreme Court overturned the Court of Appeal’s judgment in Davies v Bridgend County Borough Council [2024] UKSC 15, finding the ‘but for’ test for causation (used to establish a link between a defendant’s negligence and the claimant’s harm or loss) applies to causes of action in private nuisance, including those involving continuing nuisances resulting from the encroachment of Japanese knotweed.

Background of the case

Since 2004, Mr Davies (the “Claimant”) 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 issued a claim for damages in 2020 against the Council in Swansea County Court for it’s breach of duty in private nuisance. While the court found the Council had been in breach between 2013 and 2018, it declined to award damages to the Claimant on the basis the Claimant’s damages were irrecoverable, as the residual diminution in value was regarded as pure economic loss.

On appeal, the Court of Appeal held the Council was not responsible for a private nuisance in 2004, but the Council was liable for a private nuisance for failing to treat the Japanese knotweed from 2013 to 2018.

By quoting the case of Delaware Mansions Ltd v Westminster City Council [2001] UKHL 55, [2002] 1 AC 321 (“Delaware”), the Court of Appeal held the Council had been in continuing breach of duty over the period between 2013 and 2018 which caused the residual diminution in value of the claimant’s property, as a result of persisting encroachment. The Court awarded the claimant damages of £4,900 for the residual diminution of his property, due to the stigma of Japanese knotweed.

2024 Supreme Court’s decision

The Supreme Court granted permission to appeal and in 2024 held the Court of Appeal had misinterpreted the decision of Delaware which was that claimants can recover the reasonable costs incurred in abating a continuing nuisance. However, the Supreme Court found the diminution in the claimant’s property’s value was not a reasonable cost incurred in abating a continuing nuisance. Instead, the Supreme Court applied the ‘but for’ test for causation.

By applying the ‘but for’ test, the Supreme Court held the residual diminution in the property’s value had not been caused by the Council’s breach of duty as there was no evidence that this increased or contributed to the diminution in value of the claimant’s property during the period between 2013 and 2018.

The Supreme Court found  “This was because the JKW [Japanese knotweed] was already present on the claimant’s land before 2013 so that the residual diminution in value had already been brought about by the natural, non-actionable, encroachment of the JKW.” and that “The diminution in value would have occurred in any event so that there is no causal link between the defendant’s breach of duty and the diminution in value claimed.”

The Court concluded the claimant was not entitled to damages for the cost of treatment of the Japanese knotweed as that cost was not caused by the Council’s breach of duty, and the cost of treatment would have had to be incurred irrespective of the breach of duty.

Conclusion

The Supreme Court’s decision in Davies v Bridgend County Borough Council [2024] UKSC 15 is notable for confirming the ‘but for’ test for causation applies to causes of action in private nuisance, including those involving the continuing nuisance arising from the encroachment of Japanese knotweed.

For claimants to successfully claim damages, it is likely they will need to provide irrefutable evidence the diminution in value of their property has been caused by the other side.

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.

Japanese knotweed: Notable decision by The Supreme Court

Have a question? Contact Kate

Have a question? Contact Kate

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