Japanese knotweed – a nuisance?

Two recent County Court decisions have tackled the issue of Japanese knotweed in the context of private nuisance claims between neighbouring landowners.

It is important that NHS Trust estates teams are aware of the implications for managing large portfolios. The first dealt with two separate actions against the same defendant, Williams v Network Rail Infrastructure Ltd and Waistell v Network Rail Infrastructure Ltd (“Waistell”).

The second was a more recent judgment given in Smith and another v Line.


In Waistell, the claimants each owned one of two adjoining semi-detached houses. Network Rail owned a railway line behind those houses. There was an access path and embankment between the houses and the railway line. Japanese Knotweed had existed on the embankment for more than 50 years. The claimants alleged nuisance in two ways:

  • By physical encroachment of the Japanese Knotweed onto the claimants’ land.
  • By the presence of Japanese Knotweed on the defendant’s land.

The claimants sought injunctions requiring Network Rail to treat the Japanese Knotweed and damages, such as for diminution in the value of the claimants’ land.

The Court acknowledged that the Japanese Knotweed had encroached from Network Rail’s embankment, over the boundary to and under the claimants’ foundations, however it held that the claimants had failed to make out their claim on encroachment.

Physical damage is an essential element for a successful claim of encroachment, certainly in cases such as gradual encroachment from branches and roots in contrast to original encroachment from built projections. The claimants had not been able to show damage.

The Court instead hold that the presence of Japanese Knotweed on Network Rail’s land had unlawfully interfered with the claimants’ quiet enjoyment or use and enjoyment of their land because the value of the claimants’ land was reduced by the presence of Japanese Knotweed on Network Rail’s land even if treated and Network Rail had breached the measured duty of care it owed its neighbours to take reasonable steps to minimise a known hazard.

Each claimant received damages for the cost of a Japanese Knotweed treatment package and the diminution in value of their property.

It should be noted that Network Rail is appealing this decision.

Smith v Line

In Smith v Line, the defendant owned a large area of land and sold part of this land in 2002 to the claimants. She retained the remainder of the site to be used for grazing and as a car park. The claimants found Japanese Knotweed on their land in 2003 and complained to Ms Line.

By 2013, the claimants had successfully treated the Japanese Knotweed on their land and asked that Ms Line take steps to remove it from hers as it grew close to the boundary. Ms Line refused and stated that she thought it was encroaching from the claimants’ land.

The claimants brought a nuisance claim against Ms Line seeking an injunction or, alternatively, damages.

Joint Japanese Knotweed experts were instructed and they concluded that the Japanese Knotweed had started on Ms Line’s land and encroached onto the claimants’ land. They also confirmed that the continued presence of Japanese Knotweed left untreated on Ms Line’s land had the effect of reducing the current value of the claimants’ land by 10%.

Again the claimants argued nuisance on the basis of physical encroachment and interference with the amenity of their land based on the presence of Japanese Knotweed on Ms Line’s land.

The Court, following the judgement in Waistell, found that the claimant’s land had not been damaged but did find that Ms Line had failed to comply with her measured duty of care and that the Japanese Knotweed on Ms Line’s land interfered with the claimants’ enjoyment of their land.

Ms Line was given a mandatory injunction to enter into a contract with a reputable contractor to treat the Japanese Knotweed on her land and she was further ordered to pay the claimant’s costs.


Unless we receive a Court of Appeal decision to the contrary, it seems likely that any claim in nuisance based on encroachment of Japanese Knotweed will not succeed in the absence of physical damage to the claimant’s land.

That leaves potential claimants having to rely on the loss of amenity approach based on the diminution in value of their land by reason of a reduced market.

Either way, it is now very clear that Japanese Knotweed can be an actionable nuisance before it causes any physical damage to neighbouring land.

The cases have particular implications for large landowners such as NHS Trusts or healthcare developers, where they are trying to manage and/or control Japanese Knotweed and other invasive non-native species.

Practical tips in transactions

Identifying Japanese Knotweed on a site early will also enable landowners or developers to assess the cost of their options for treatment and any possible delay to their development programme linked to required treatment.

This will ensure that the development could be restructured to allow for treatment and reduce impact on the timetable, for example by introducing phasing to the programme. It will also enable to developer to negotiate any reduction in price, where appropriate.

When investigating a new development site, developers should instruct their solicitor to raise a specific enquiry asking the seller to confirm the presence of Japanese Knotweed on the site or any neighbouring land. This subject is not adequately dealt with in standard pre-contract enquiries at the moment.

Lenders are likely to be reluctant to lend on land with Japanese Knotweed close to its borders and thorough inspection for Japanese Knotweed on not only any land being purchased but also all neighbouring land should be undertaken at the outset of any new transaction. Buildings insurance policies generally do not cover damage and problems caused by Japanese Knotweed. It will be necessary to obtain a guarantee from any company employed to treat or eradicate it from a site.

From another perspective, Sellers equally should be careful to ensure that they reveal any past Japanese Knotweed treatments within their replies to pre-contract enquiries.

This is the case even where the seller believes that they have eradicated the issue. Sellers should be aware that any reply of ‘not so far as the seller is aware’, could hold them liable for misrepresentation where they have not made reasonable efforts to check the position and there is a subsequent Japanese Knotweed outbreak.

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