Generally, there are two types of case. Claims brought by property purchases against vendors’ who have failed to disclose its presence and claims by land owners against neighbours where knotweed has spread from adjacent land. This article concentrates on the second category.
In Williams & Waistell v Network Rail the owners of two houses brought a claim against Rail Track because knotweed had spread from the Defendant’s land into their gardens. The house owners claimed damages based on private nuisance and, at first instance, succeeded on the ground that there had been an unlawful interference with their enjoyment of their property. An alternative claim based on encroachment failed because there was no actual physical damage to their houses.
The Defendant appealed and the decision of the court of appeal has now been published (Network Rail Infrastructure v Williams & Waistell  EWCA Civ 1514). The Defendant’s principal challenge was against the Recorder’s conclusion that pure economic loss (diminution in the value of the Claimants’ properties) was actionable in private nuisance on the basis that it interferes with the quiet enjoyment of a Claimant’s property.
On this point the Court of Appeal agreed with them, explaining that the purpose of the tort of nuisance is not to protect the value of property as an investment but to protect a land owner’s enjoyment of their property and did not extend to pure economic loss. However, the court also reconsidered the Recorder’s dismissal of the encroachment claim. Reversing his decision, they found that the presence of knotweed not only carries the risk of future physical damage to buildings and structures but that the mere presence of its rhizomes imposes an immediate burden on the owner of land in terms of an increased difficulty to develop (and in the cost) should the owner wish to do so. The court concluded that there is no reason why the legal position concerning nuisance caused by the encroachment of the branches or roots of trees should undermine the right of the Claimants’ to claim damages for nuisance by reason of the encroachment of Japanese knotweed.
The net effect of this decision is that it should now be easier for a landowner to bring a knotweed claim against a neighbour.