Japanese Knotweed: What has changed following the Supreme Court’s Decision in Davies v Bridgend County Borough Council 2024

The History

Mr Davies bought his property in 2004. Mr Davies’ property adjoins land owned by Bridgend County Borough Council. Japanese Knotweed growing on the Council’s land encroached onto Mr Davies’ land. Mr Davies brought a claim for nuisance against the Council and sought, amongst other things, damages for diminution in value amounting to £4,900.

In 2023, the Court of Appeal held that the Council were in breach of its duty of care to Mr Davies and that once there is physical encroachment, damages for diminution in value were available.

The Supreme Court Decision

The Supreme Court found a number of issues with the Court of Appeal’s conclusion.

When Mr Davies purchased his property in 2004, Japanese Knotweed had already encroached from the Council’s land but greater awareness of the risk of damage by Japanese Knotweed only became public knowledge following the issue of the RICS information paper in 2012, 8 years later.

This means that an actionable private nuisance only arose in 2013 when the Council were aware of the risk of damage as a result of the Japanese Knotweed, but had also failed to effect a reasonable and effective treatment programme. This nuisance continued until 2018 when the Council took steps to treat the Japanese Knotweed.

The Supreme Court indicated that the main issue in this case was causation and whether the diminution in value was caused by the Council’s breach of duty in private nuisance.

The Supreme Court applied the “but for” test and asked “would the diminution in value have occurred “but for” the breach of duty of the Council between 2013 and 2018?” The answer to this question is no; the diminution in value occurred long before the breach by the Council in 2013. Accordingly, the Council’s breach of duty is eliminated as a cause of the diminution in value.

What does this means for property owners?

The Supreme Court’s decision was not a complete overturning of the Court of Appeal’s prior decision. Encroachment of Japanese Knotweed is still an actionable nuisance and the decision in this case does not prohibit the possibility of a claim for diminution in value. A claim may also still be possible if the continued encroachment of Japanese Knotweed causes further diminution in value notwithstanding that the encroachment first occurred prior to 2012.

However, if the Japanese Knotweed has already encroached prior to 2012, the defendant may now have an argument that the loss has occurred before they were in breach of their duty in private nuisance. This is likely to be a particularly useful decision for Local Authorities and rail operators who own land where this invasive plant can often be found growing.

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