Japanese Knotweed and Liability – Clarity in the Law?

Following a recent Court of Appeal decision originating from a decision handed down at the Cardiff County Court, some clarity has been provided on the question of liability in respect of Japanese Knotweed and its spread to adjoining land or even allowing knotweed to grow near properties.

Japanese knotweed or Fallopia Japonica is a large, herbaceous perennial plant, with hollow stems and distinct raised nodes giving it an appearance similar to bamboo, even though it is not related. Broad, oval truncated leaves with white or cream flowers made this a plant the Victorians believed would be an ornamental feature in 19th Century British gardens. Victorian engineers also saw the benefit of knotweed in light of the industrial revolution, perceiving that the strength of the root structure could be used to support and hide railway embankments. However, the significant damage such a root structure can cause to buildings was unknown to the Victorians.

The presence of knotweed and the approach to treating such growth means this once ornamental plant is now classed as such a dangerous plant with it being an offence to try to dispose of any knotweed contaminated soil unless done so by trained operatives and in supervised, specified treatment areas. Property owners must disclose the presence of knotweed as part of any sale process and having such growth on land could result in potential issues with any lender. What was an ornamental plant is now a significant issue for any potential house sale as sellers can expect the value of their land to diminish with the presence of knotweed, that is, if a buyer is willing to buy the property or land knowing of the presence of it.

County Court Decision

The Cardiff County Court’s ruling in May 2017 in the combined decision of Waistell v Network Rail Infrastructure Ltd and Williams v Network Rail Infrastructure Ltd (2017), made Network Rail liable in nuisance for damage caused to the Claimants’ properties due to the growth of knotweed on the adjoining railway embankment. The Claimants alleged Network Rail were responsible for the embankment and the knotweed growth upon it, along with the spread of its root network which was alleged to be causing damage to their properties. The failure to prevent such a spread of growth made Network Rail liable for such damage, according to the Claimants.

The Court agreed with the Claimants, awarding damages for the encroachment of knotweed on to their properties as well as the cost of a treatment programme and insurance backed guarantees for such a programme. Both claimants were awarded damages for the diminution in value of their properties once the treatment of the knotweed had taken place. Such a decision was the first known decision from a Court on the question of liability of a landowner for the spread and liability of knotweed on adjoining land. Network Rail appealed the decision to the Court of Appeal.

Court of Appeal Decision

On appeal, the Court upheld the original decision against Network Rail, making them liable for the Japanese Knotweed which had encroached from the nearby railway embankment into the properties of the claimants.

However, the Court agreed with Network Rail they could not be liable for any diminution in value as the properties had not been damaged. The Appeal Judges agreed the original decision was incorrect on the property damage head of claim but agreed that Network Rail were liable for the other losses and for their failure to contain the spread of knotweed onto the Claimants’ properties.

[Having knotweed spread from an area outside the control of the property owner was likely to cause damage to the land the Court found, even if no structural damage had been caused to the property. The mere fact that the landowner where the knotweed grew and who had permitted such knotweed to spread to adjoining land made the landowner liable for the costs of remediation and damage in the Court’s view.]


Whilst this decision has certainly clarified an area of law which had previously failed to provide any meaningful clarity on liability of landowners for Japanese knotweed, the decision fell short of the Claimant’s views that damages and compensation for damage to their properties should be paid for allowing such a spread of knotweed from adjoining land. On this, it appears that both Claimants are reviewing their position and likewise Network Rail in light of the Court’s decision. There may well be further appeals on this matter in future in light of the decision.

If you are aware of the presence of knotweed encroaching or growing on your land which has emanated from adjoining land, the landowner should be informed immediately of the problem. Treatment for such growth will certainly limit and prevent further growth and spreading of the knotweed and trained operatives should deal with such a growth to prevent any further issues arising.