The Supreme Court has handed down its eagerly anticipated judgment in Davies (Respondent) v Bridgend County Borough Council (Appellant) [2024] UKSC 15.


Davies concerned nuisance due to encroaching Japanese knotweed (“JKW”). Mr Davies, the claimant, purchased his Bridgend property in 2004. Before that date, JKW had spread from the adjacent land owned by the defendant, Bridgend Borough Council, onto the property Mr Davies would come to purchase.

As at 2004, the encroachment by JKW onto Mr Davies’s property was not an actionable private nuisance. It became actionable in 2013. That is because, it was only in 2013, that the Council was or should have been aware of the risk of damage and loss of amenity to Mr Davies’s property given publicly available information about JKW. Notwithstanding this information, the Council did not implement a reasonable and effective treatment programme in relation to the JKW which the Council knew, or should have known, was growing on the Council owned land.

A reasonable and effective treatment programme was only instigated by the Council in 2018.

Decision at First Instance

In Swansea County Court, Mr Davies sought damages for diminution in the value of his property. Whilst the district judge determined that the Council was in continuing breach between 2013 and 2018, the judge declined to award damages, concluding that damages for diminution in value were irrecoverable.

Appeals Below

The decision at first instance was upheld on appeal. On a further appeal, the Court of Appeal upheld the finding of continuing breach but found that damages for residual diminution of the value of Mr Davies’s land of £4,900 were recoverable.

The Supreme Court’s Decision

In a unanimous decision, the Supreme Court allowed the appeal finding that the diminution in value of Mr Davies’s land was not caused by the Council’s breach having applied the “but for” test.

Simply put, the “but for” test is used to ‘eliminate irrelevant causative factors’ [56].

In Davies, the Supreme Court posited this question: would the diminution in value have occurred but for the Council’s breach of duty of the defendant between 2013 and 2018?

The answer to the “but for” question was no. The diminution in value had crystallised before the Council’s breach of duty in private nuisance – ergo, before 2013 [70].

Mr Davies also argued that he was entitled to damages due to the diminution in value arising from the ‘stigma’ of JKW. Mr Davies argued that the stigma lessens over time; so, too, does the diminution in value [9]. Mr Davies criticised the Council and said that commencement JKW treatment in 2013 – rather than 2018 – would have meant that the stigma, and the corresponding diminution in value, would have decreased by 2018. Therefore, Mr Davies argued, an award should have been granted for the difference between the amount of diminution in value in 2018, and the amount that it would have been in 2018 if the Council had commenced treatment in 2013.

Mr Davies’s position was that given the Council had failed to provide evidence of what the lower figure should be, Mr Davies should have been awarded the full amount of £4,900 in respect of the diminution in value. The Supreme Court found that this was something for Mr Davies, as claimant, to prove.

Once more, the Supreme Court applied the “but for” test and found that the answer was negative: the Council’s breach of duty from 2013 did not cause the residual diminution in value of the land. JKW was on the Council’s land prior to 2013 so that “the residual diminution in value had already been brought about by the natural, non-actionable, encroachment of the Japanese knotweed” [85].

Significance of the Supreme Court’s Decision

Whilst deciding a narrow point arising in the encroachment of JKW, and damages of a modest sum, the Supreme Court offers a powerful restatement of the “but for” test, taking in a gamut of cases which underline the principle from far outside private nuisance cases: Barnett v Chelsea and Kensington Hospital Management Committee [1969] 1 QB 428, Performance Cars Ltd v Abraham [1962] 1 QB 33 and Kerry v England [1898] AC 74 to name three.

The Supreme Court decision is essential and certain reading for civil practitioners examining “but for” causation.