Japanese Knotweed in the Supreme Court – no diminution in value

13 May 2024

The Supreme Court delivered a minor blow to claimants in cases involving Japanese Knotweed last week when it handed down its judgment in Davies v Bridgend County Borough Council [2024] UKSC 15. However the case has wider implications for residual diminution in value cases.

Background to the case

Knotweed from the council’s land had encroached onto Mr Davies' land, which he had owned since 2004. In 2012, a Royal Institute of Chartered Surveyors report described the difficulties the plant could cause.

In 2014, the council had actual knowledge of the presence of knotweed on its land in close proximity to Mr Davies’ land. However it only took steps to treat it in 2018.

In 2017, Mr Davies tried to sell his property and learnt of the knotweed issue. He sued.

History of the claim 

At trial, the District Judge found that:

  • encroachment would have occurred before 2004
  • the council had constructive knowledge of this in 2012/2013, and
  • the council had committed a private nuisance from 2013 to 2018.

The judge dismissed all the claims, including, importantly, a claim for residual diminution in value (claimed at £4,900).

This judgment was upheld on appeal to the Circuit Judge. Those courts agreed with the council that the presence of the knotweed in 2004 was way before the breach of duty occurred. Any “stigma” attached to Mr Davies' land was caused before the breach.

However, the Court of Appeal took a different view relying on Delaware Mansions Ltd v Westminster City Council [2001] UKHL 55, [2002] 1 AC 321. The harm was caused at the end of the period of continuing breach (2018).

The council appealed and Network Rail intervened.

Supreme Court’s judgment

In short, the Supreme Court applied the famous “but for” test for causation. If the damage in question would have occurred before the breach, then there is no causation. In this case, it was therefore crucial that there was no evidence the breach between 2013 and 2018 increased the diminution in value.

What does the judgment mean for you?

Claimant solicitors would  be wise in appropriate cases to ask experts to consider whether a delay in treatment has affected the residual diminution in value.

If you would like advice on Japanese Knotweed cases, or those involving diminution in value generally, please contact me or alternatively contact my clerks.