The new claims trend spreading like Japanese knotweed

Last year, the ground-breaking nuisance case, Network Rail v Williams & Waistell (Williams), established there did not need to be physical damage to bring a claim for encroachment of Japanese knotweed (JK), leading to an increase in the number of JK claims against landowners and their insurers. However, renewed interest on the impact of JK, including a recent study and government enquiry, has the potential to affect the scope of this fast-spreading claims trend.


JK was first introduced into the UK as an ornamental plant and animal feed but its ability to thrive, spread quickly, and cause apparently widespread damage has led to it being described by the Environment Agency as ‘indisputably the UK’s most aggressive, destructive and invasive plant’.

A key feature of JK is its rhizomes, which are underground stems similar to roots. An entire plant can regrow from a very small section of rhizome, which can lay dormant for many years in the soil before growing again. Because of this, JK is classed as controlled waste and treatment of JK is heavily regulated. The process to eradicate can be extremely difficult and costly and it is commonplace for lenders to refuse to offer mortgages on properties where JK is present or even nearby.

If a landowner allows JK to spread onto neighbouring land, they face a potential nuisance claim. Until Williams, general thinking was that encroachment of naturally occurring vegetation was not actionable until physical damage occurred. That is no longer the case for JK, as Williams reshaped the legal landscape and opened the door on a number of claims that previously were not viable.

The Williams decision

Mr Williams and Mr Waistell (the claimants), owners of adjoining bungalows, backed onto land owned by Network Rail (NR), which contained JK. There was some encroachment and the claimants brought a private nuisance claim against NR, seeking damages and an injunction for NR to treat and eliminate the JK.

At first instance, the encroachment claim failed, as there was no physical damage. However, the claim for loss of quiet enjoyment succeeded as the presence of JK on NR’s land had reduced the market value of the properties and as such, the claimants were awarded damages.

NR appealed and the Court of Appeal upheld the damages award albeit for different reasons. They confirmed that whilst nuisance claims did not protect the value of property, the presence of rhizomes in the claimants’ soil was an interference with the enjoyment of land and as such, proof of physical damage was not required. The rhizomes imposed a burden on the claimants because any work requiring removal of the contaminated soil was likely to be specialist and costly and it diminished the ability to use and enjoy the land.

Government enquiry

On 19 November 2018, the government launched an inquiry into JK’s impact on the built environment. Twenty-seven interested parties provided written evidence, including NR, and numerous parties gave oral evidence at a panel discussion on 22 January 2019. The responses expressed concern that limited research had been undertaken on JK in the last twenty years and that updated guidance may be needed.

Part of the evidence included a recent study undertaken by AECOM and Leeds University, which found that the propensity for JK to cause physical damage to properties has been vastly over-estimated. The study asserted that direct damage from other plants and trees, is just as likely, if not more, to occur and that rhizome spread was not as extensive as currently reported.

The government’s response is awaited, although we expect to hear from them before the end of the year.


In Williams, the Court of Appeal was keen to point out that JK carried with it “the risk of future physical damage to buildings, structures and installations on the land”. Evidence from the Leeds University study suggests this risk is overstated and understanding may change in the future.

However, the court’s primary rationale for the claim succeeding is the increased burden and cost on a landowner by virtue of having rhizome-contaminated soil. Accordingly, whilst the government might determine that the risk of physical damage from JK is lower than currently perceived, this does not appear to address the real concern: contaminated soil is still controlled waste. As long as current legislation puts a landowner to extra burden in using, or developing on, contaminated soil, encroachment - even without physical damage - is likely to remain an actionable nuisance.

It is therefore difficult to see how the outcome of the government enquiry will do much to halt the cascade of claims set in motion by Williams, without significant parliamentary intervention (amending the relevant legislation). Large landowners and their insurers should therefore be prepared to manage and respond to this emerging liability risk, at least for the foreseeable future.

The only silver lining is the possibility of residual diminution in value claims reducing over time, if the perception of the risks posed by JK is altered.

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