Japanese Knotweed: 2023 Update

  • Legal Development 12 September 2023 12 September 2023
  • UK & Europe

  • Casualty claims

In February 2023, the Court of Appeal handed down its judgment in Davies v Bridgend County Borough Council. A key finding from that judgment was that diminution in value was recoverable by the Claimant, notwithstanding that the knotweed had encroached onto their land before the Defendant could reasonably be expected to have known about the knotweed; provided that the Defendant had subsequently breached its duties, it would be liable to pay residual diminution in value.

This judgment has received some criticism – even if the Defendant had not subsequently breached its duties, the Claimant would still have to reveal a past history of Japanese Knotweed on selling the property on the TA6 form, and so would have suffered residual diminution in value in any event.  The Defendant has been given permission to appeal the judgment to the Supreme Court.  We are waiting to hear when this will take place.

We had seen lower numbers of claims and claims falling away or discontinued since the publication of RICS 2022 guidance. The main reason for this is that the new guidance advises that in most cases, JKW can be effectively controlled by herbicidal treatment and there should be no restriction on lending. The guidance also states that any residual diminution in value (after treatment) of land should not be calculated as a blanket percentage but considered on a case by case basis; often the value of residual blight will be very low or nil.   Until that new guidance, claimant solicitors often applied a “standard” 10% of total value of property, as this was the figure awarded in Williams & Waistell v Network Rail. It is now clear that 10% is no longer a one-size-fits-all sum, although we have seen some County Court judges awarding 5% without a detailed consideration of the valuation evidence adduced.  

We have also seen an increase in claimants alleging that it is necessary to excavate the Japanese Knotweed from their garden so that they can fulfil ambitious landscaping schemes.  As the costs of excavation can be many times more expensive the costs of herbicide treatment, it appears that claimant solicitors are hoping that even if the residual diminution in value element of a claim is reduced, the award for treatment costs will be higher.  We are resisting these claims where there are no obvious reasons (such as plans to extend the property over affected land) why excavation should be allowed.  However, ultimately, judges will decide these claims based on whose witness and expert evidence they prefer. 

Unfortunately, since the judgment in Davies v Bridgend we have seen the revival of some old claims, which we had previously successfully “batted away” on the basis that the knotweed had spread to the claimant’s land long before the defendant could reasonably have prevented this.  The finding in Davies v Bridgend is now often referred to in correspondence and pleadings.  

A further reason for claims being revived, and why we expect see an uptick in the number of claims issued before 1 October 2023, is that a new fixed costs regime will apply to almost all claims valued at less than £100,000 which are issued after that date.  The operation of the fixed rate regime is complicated – the amount which a successful party is entitled to recover will depend upon the stage the claim reaches and how complex it is considered to be – but are expecting to see a significant reduction in costs payable to claimant solicitors. 

It remains the case that the strongest overall defences to Japanese Knotweed claims is where treatment has been commenced promptly following notice and has been maintained in the following years.  Transport authorities often have excellent records in this regard; local authorities and housing associations are sometimes comparatively behind the curve. Where there are gaps in treatment, an early negotiated settlement is often advisable. 


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