Council wins Supreme Court appeal in landmark Japanese knotweed case

The Supreme Court has allowed a Welsh council's appeal in a dispute over the diminution in value of land arising from the encroachment of Japanese knotweed.

In Davies v Bridgend County Borough Council [2024] UKSC 15 the justices concluded that the diminution in value of the claimant's land was not caused by the defendant council's tortious conduct, and no damages should be awarded.

[What follows is based on the Supreme Court's press summary]

The background to the appeal was that, at some date well before Mr Davies, the claimant, purchased his land in Bridgend in 2004, Japanese knotweed spread from land owned by the council onto the land now owned by the claimant.

In 2004, encroachment of Japanese knotweed onto neighbouring land was not an actionable private nuisance.

An actionable private nuisance arose in 2013 when the defendant council was, or ought to have been, aware of the risk of damage and loss of amenity to the claimant’s land as a result of publicly available information about Japanese knotweed at the time, and it failed to implement a reasonable and effective treatment programme in relation to Japanese knotweed which it knew or ought to have known was growing on its land.

The Supreme Court said it was not until 2018 that the defendant implemented a reasonable and effective treatment programme.

Mr Davies brought a claim for damages against Bridgend in Swansea County Court. The district judge found that the defendant was in continuing breach between 2013 and 2018 but declined to award damages because he held that damages for diminution in value are irrecoverable. On a first appeal, the district judge’s ruling was upheld.

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 the claimant’s land (said to be £4,900) were recoverable.

The council appealed to the Supreme Court.

In a decision handed down today (8 May 2024), Lord Reed, Lord Lloyd-Jones, Lord Burrows, Lord Stephens, and Lady Simler unanimously allowed the appeal.

Lord Stephens gave the lead judgment, with which the other Justices agreed.

Lord Stephens said that in the tort of private nuisance involving encroachment of Japanese knotweed from the defendant's land onto the claimant's land, the claimant is required to establish that the defendant's breach of duty did in fact cause the loss suffered. 

In considering causation, the purpose of the "but for" test is to eliminate irrelevant causative factors, he added.

The Supreme Court judge said that in the context of this case the 'but for' test asks: would the diminution in value of which the claimant complains have occurred 'but for' the breach of duty of the defendant between 2013 and 2018? 

Lord Stephens said that if the diminution in value would have occurred in any event, then the defendant's breach of duty was eliminated as a cause of the diminution in value so that there would be no causal link between the defendant's breach of duty and the diminution in value.

The Supreme Court found that the answer to the "but for" question in this case was to be seen in the context that there was no  evidence and no finding by the district judge that the defendant's breach of duty between 2013 and 2018 had increased or materially contributed to the diminution in value of the  claimant's land. 

In that context the answer to the "but for" question was simply that the diminution in value had occurred long before any breach by the defendant of the relevant duty in private nuisance first occurred in 2013.

"Accordingly, the application of the 'but for' test in this case eliminates the defendant's subsequent breach of duty as a causative factor," Lord Stephens said.

"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 Supreme Court therefore allowed the appeal on this ground, and no damages were awarded.

Mr Davies had raised a further point that he should be entitled to recover damages in respect of diminution in value because the stigma causing the diminution decreases over time with the consequence that the amount of diminution in value also decreases over time.

He argued that if Bridgend had commenced treatment of the Japanese Knotweed in 2013 instead of in 2018 then the stigma and the resultant amount of diminution in value would have decreased by 2018 - and therefore, an award should be made for the difference between the amount of diminution in value in 2018 and the amount that it would have been in 2018 if treatment had commenced in 2013. 

The claimant argued that in the absence of evidence from the defendant demonstrating what the lower figure should be awarded, he should recover the full amount of £4,900 in respect of the diminution in value. 

However, Lord Stephens said: "The duty of a trial judge is to consider the matters which are in issue on the pleadings, and which are supported by evidence, and only those matters. As I have indicated the claimant's further issue was not pleaded and there was not one word of evidence to support it.

"Furthermore, the onus of proof remained on the claimant to establish the difference between the amount of the diminution in value in 2018 and the amount that it would have been if treatment had commenced in 2013. In my view the district judge would have acted quite improperly if he had made any award in favour of the claimant on a hypothesis, not pleaded and not supported in evidence, that the stigma causing the diminution decreases over time with the consequence that the amount of the diminution in value also decreases over time. In my view the hypothesis amounts to no more than conjecture.

"I reject the submission that an award of damages in relation to diminution in value can be supported on the basis of the further issue raised by counsel on behalf of the claimant."

In a concurring judgement, Lord Burrows added that the question to be answered in this case was whether the relevant damage required to establish the tort of private nuisance was factually caused by the breach of duty where the same damage was present prior to the breach of duty.

Applying the "but for" test to the facts of this case, the breach of duty from 2013 did not factually cause the residual diminution in value of the land, Lord Burrows said.

The claimant had not proved that the residual diminution in value would not have been suffered but for the breach of duty, he added.

This was because the 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 Japanese knotweed.

Adam Carey