Supreme Court judgment 8 May 2024. Were the lower courts correct to decide that loss suffered by the Respondent, in the form of diminution in value of the Respondent's property as a result of the encroachment of Japanese knotweed from the Appellant's land, was caused by the Appellant's breach of duty in failing to treat the knotweed, in circumstances where the encroachment first arose before the Appellant's breach? Decision, appeal allowed: the fact that the encroachment had existed when he bought the property, at a time before an actionable tort in private nuisance arose, meant that the neighbour's failure to treat the knotweed had not in fact materially contributed to the diminution in value. The application of the "but for" test eliminated the neighbour's subsequent breach of duty as a causative factor: the fact that the diminution in value would have occurred in any event meant that there was no causal link between the breach of duty and the diminution in value claimed.

Judges: Lord Reed, Lord Lloyd-Jones, Lord Burrows, Lord Stephens, Lady Simler

Judgment appealed [2023] EWCA Civ 80