The Court of Appeal judgment in this case has been released, and it has attracted a lot of interest from Claimant firms, insurers and large land owners/local authorities.

The appealed focused on the issue of diminution of land which has been infected by Japanese Knotweed. “JKW”.

The Facts:

  1. The Defendant had JKW on its land for over 50 years;
  2. In 2004 the Claimant bought a property on neighbouring land;
  3. The spread of JKW to the Claimant’s land had occurred prior to 2004.

The Claimant became concerned about the knotweed in 2017 and raised this with the Defendant in 2019.

The District Judge at first instance found the Defendant was in breach of the relevant duty for a period starting from 2013, when it was accepted by the Judge that the Defendant should have had knowledge of the JKW growth, and lasting until 2018 when a reasonable an effective treatment programme started.

However, the District Judge rejected the Claimant’s claim that he was entitled to damages for “residual diminution in value” of his property, a loss which the Claimant said arose even though the JKW had been treated effectively. The District Judge concluded that this was economic loss only, and therefore irrecoverable.

That decision was upheld by a High Court Judge on a first appeal.


The Claimant appealed the “residual diminution” point to the Court of Appeal.

In allowing the appeal, the Court of Appeal stated that, despite successful treatment, the encroachment of JKW onto his land had represented an ongoing nuisance, and that such encroachment would have affected the Claimant’s use and enjoyment of his land, thereby amounting to “damage” to the property.

As such this was not a case of pure economic loss, and the “residual diminution” could be recovered as damages.


The judgment has attracted a lot of headlines suggesting that diminution claims in JKW cases will increase.

However the judgment is not all bad news for Defendants.

The Court of Appeal considered recently updated guidance from RICS which suggests that JKW is not as damaging as previously considered. This represents a softening of the RICS position from the previous guidance on JKW published in 2012.

The Court of Appeal found that as JKW is not as indestructible and harmful to buildings as previously thought, trivial or de minimis encroachment of JKW would not be actionable. Only the spread of JKW in excess of a de minimis level will be recoverable. This is a significant movement, and should continue the process of demystifying JKW, although the Court stopped short of defining what would amount to trivial or de minimis spread.

The decision also re-iterated the principle that the law of nuisance is not intended to protect the value of land, and simply having JKW proximate to land does not give rise to a claim. There still has to be a level of escape to the Claimant’s land for there to be an actionable nuisance.

The updated RICS guidelines outline a suggested methodology for surveyors considering the impact of JKW and it seems likely that adherence to these suggestions will become increasingly important to convince the Court as to the appropriate level of diminution. Defendants would be advised to consider diminution as a valid head of loss and to focus on the quantification of that loss by a suitable expert.


The appropriate valuation of these claims will continue to be a key contentious issue, which is likely to become only more significant once the extended fixed cost regime comes into force. For now, it is likely that JKW claims will remain a nuisance for insurers and local authorities alike.

Our use of cookies

We use necessary cookies to make our site work. We'd also like to set optional analytics cookies to help us improve it. We won't set optional cookies unless you enable them. Using this tool will set a cookie on your device to remember your preferences. For more detailed information about the cookies we use, see our Cookies page.

Necessary cookies

Necessary cookies enable core functionality such as security, network management, and accessibility. You may disable these by changing your browser settings, but this may affect how the website functions.

Analytics cookies

We'd like to set Google Analytics cookies to help us to improve our website by collection and reporting information on how you use it. The cookies collect information in a way that does not directly identify anyone.
For more information on how these cookies work, please see our Cookies page.