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Japanese Knotweed, Damages and the Supreme Court - Davies v Bridgend County Borough Council [2024]

17th May 2024

The focus of this week’s Legal Update looks at the decision handed down earlier this month by the Supreme Court on the issue of claims against neighbouring owners for compensation arising from the invasion of Japanese Knotweed, something relevant to any owner of land.

The Supreme Court allowed the Council’s appeal where the owner of land neighbouring the Council's land had brought proceedings for damages in nuisance, after discovering the presence of Japanese knotweed on the Council's property and that that could have an adverse effect on the sale value of his own property.

The background

In Davies v Bridgend County Borough Council [UKSC 2023/0028], the Claimant in the proceedings, Mr Davies, purchased the property at 10 Dinham Street, Bridgend (“the Property”) in 2004. Some 13 years later in 2017, Mr Davies discovered the existence of Japanese Knotweed (“the Knotweed”) at the Property - Japanese Knotweed being a fast growing and invasive weed that can cause substantial damage to land and buildings if not properly treated and eradicated which itself costs the land owner a not inconsiderable sum.

Whether or not Japanese knotweed is present at a property is a question frequently posed during the sales process and its existence, if known, must be disclosed.

Soon after Mr Davies knew of the existence of Knotweed at the Property, he brought proceedings against the Council seeking damages, alleging a breach of duty under the tort of nuisance towards him because the Knotweed had encroached from Council owned land onto his.

The damages sought by Mr Davies included the cost of treating the Knotweed in order to control it but also a sum of £4,900.00 in respect of the diminution in value of the Property.

Mr Davies’ head of claim for the treatment costs was dropped in advance of trial as he eventually accepted that the treatment was required before he purchased in 2004.

The lower court decisions

At trial, one of the issues was whether Mr Davies was entitled to recover £4,900.00 as damages from the Council for residual diminution of the Property. The Judge dismissed Mr Davies’ claim.  

However, upon appeal of that decision to the Court of Appeal, the Judges found in favour of Mr Davies, determining that the Council was committing a continuing breach of duty between 2013 and 2018. The relevance of the 2013 date is that in 2012, the Royal Institute of Charted Surveyors published a guidance paper that detailed the risk of damage that Japanese knotweed could cause to a building and the need to treat and control it.  Prior to that report there was no actionable nuisance by one landowner against another for the encroachment of Japanese Knotweed.  After the report though that position reversed and there was potential culpability for the landowner from whose land the Knotweed spread.

The Court of Appeal reasoned that as the residual diminution in value was harm which occurred at the end of the period of continuing nuisance, it was harm caused by the continuing breach.   The Court of Appeal therefore over turned the lower court decision and awarded Mr Davies’ £4,900.00.

The Supreme Court decision

On appeal by the Council to the Supreme Court, the decision of the Court of Appeal was reversed and the Judges found that no damages at all were payable by the Council to Mr Davies.

The Supreme Court determined that the key issue was not whether damages for diminution in value were recoverable by Mr Davies from the Council but, rather, what were the consequence of finding that the Council had not been aware of the Japanese Knotweed before 2013.

On the evidence, it was proven that the Knotweed had spread to the Property well in advance of 2004, which at that time did not give rise in law to an actionable nuisance.  Crucially, it was not part of Mr Davies’ claim that the inadequate treatment during the five-year period between 2013 - 2018 had worsened the spread of the Knotweed.  Accordingly, what followed was that any diminution in value arose from the 2004 spread, and not the period of inadequate treatment.

The significant importance of the Supreme Court’s decision is that it has reiterated the relevance of the “but for” test in causation - a very important factor in establishing a claim in nuisance. The question posed was “but for” the inadequate treatment in 2013 - 2018, would the diminution in value of the Property have occurred?  When looked at it from that perspective, it was clear that there was no link between the breach of duty and the diminution in value sought.  An adverse effect on the value of the property which occurred in or prior to 2004 and thus prior to the Council’s breach by inadequate treatment between 2013 (following the RICS report on Knotweed) and 2018 cannot form part of any award of compensation to the neighbouring land owner.


From a landowners’ perspective, the Supreme Court decision should come as welcome news as it has determined that where a neighbouring owner has suffered damage to their property through the spread of Japanese Knotweed, that does not automatically mean that the owner of the land from whose land the Knotweed emanates will be fully liable for all losses that the affected neighbour may have suffered just because, at one time, the land owner was in breach of their duty in treating the Japanese Knotweed.

Any level of damage that a landowner may be liable for is likely to be limited that those losses that are identifiably caused by the breach of duty, and which might include an increase in treatment costs and/or possibly, increased diminution where the increase is attributable to the breach of duty.

As cautionary advice, for those landowners with large portfolios, it will almost be practically impossible to routinely inspect their land for the presence of Japanese knotweed - those with smaller portfolios may not find it as difficult.   However, where Knotweed is found, whether upon inspection or notification from an affected owner of adjoining land, reasonable steps should be taken as soon as possible in order to treat it.  Doing so will reduce any risk to the landowner that may give rise to similar damages claims from owners of adjoining land.

In other words, if Japanese Knotweed is present, take all steps to deal with it!

For more information, please feel free to contact a member of the team on 01435 897297 or 


This Legal Update describes the position in law as at the date of this article and care should be taken to note any subsequent amendments to the position as set out above.  The Legal Update is provided free of charge for information purposes only; it does not constitute legal advice and should not be relied on as such. No responsibility for the accuracy and/or correctness of the information and commentary set out in the article, or for any consequences of relying on it, is assumed or accepted by any member of KDL Law or by KDL Law as a whole. 

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