Q&A: Nuisance by knotweed

Vibuhti Parmar and Aaron Walder look at the knotty problem of Japanese knotweed.

Question

In 2004, I purchased the freehold of a terraced house with a rear garden in Wales. My neighbour had Japanese knotweed in their garden, which was growing into my garden well before 2004. My neighbour didn’t implement a reasonable and effective treatment programme until 2018. Do I have an actionable claim against my neighbour? 

Answer

Yes, you may have a claim for breach of duty in private nuisance against your neighbour. 

Explanation

The tort of private nuisance would be committed where your neighbour’s activity or their state of affairs for which they are responsible unduly interferes with the use and enjoyment of your land. This would usually be a substantial and unreasonable interference. The tort of private nuisance was considered in the leading cases of Fearn and others v Board of Trustees of Tate Gallery [2023] UKSC 4; [2023] EGLR 14 and Jalla v Shell International Trading and Shipping Co Ltd [2023] UKSC 16; [2023] EGLR 24. 

Here, the Japanese knotweed encroaching into your garden from your neighbour’s garden would be an interference with the use and enjoyment of your land. An actionable private nuisance would have arisen in 2013, however, rather than 2004, as this is when your neighbour was or ought to have been aware of the risk of damage to your property due to publicly available information about Japanese knotweed at the time. This was the conclusion reached in the recent Supreme Court decision of Davies v Bridgend County Borough Council [2024] UKSC 15; [2024] PLSCS 86, where it determined that there was a breach of duty by the neighbour and an actionable continuing nuisance between 2013 and 2018. 

The tort of private nuisance is actionable only on proof of damage – which can be physical but also include other factors which interfere with the use and enjoyment of land, such as noise, smells, vibration, etc.

Question

I would also like to claim damages from my neighbour for residual diminution in value to my property of £50,000. Am I entitled to this? This is despite the treatment programme which resulted in the Japanese knotweed no longer growing into my garden. 

Answer

Unless you are able to demonstrate that there was further or a specific diminution in value between 2013 and 2018 caused by your neighbour’s breach of duty, the answer is no. This is because the diminution in value occurred before the breach of duty which commenced in 2013.

Explanation

The main issue to consider is one of causation and whether the residual diminution in value was caused by your neighbour’s breach of duty in private nuisance. 

In Davies, while the Court of Appeal had awarded the sum of £4,900, the Supreme Court unanimously overturned this and considered that the “but for” test applied – would the diminution in value have occurred “but for” the breach of duty by the neighbour between 2013 and 2018? 

The purpose of the “but for” test is to eliminate irrelevant causation factors. If the diminution in value would have occurred in any event, then the neighbour’s breach of duty is eliminated. 

Here, it appears that the encroachment of the Japanese knotweed, and therefore the diminution in value to your property, occurred before your neighbour’s breach of duty commenced in 2013. If the loss precedes the breach of duty, it cannot be said to have caused the loss. You may, however, be able to claim for diminution in value if you are able to show a causal link between the diminution in value of the property and your neighbour’s breach of duty, ie produce evidence that the breach of duty between 2013 and 2018 increased and/or materially contributed to the diminution in value. 

The failure of your neighbour to treat the land between 2013 and 2018 is likely to have increased the spread of Japanese knotweed and so it is possible that you may be able to evidence a diminution in value for this period. The burden of proof in this respect would lie with you, as the potential claimant. In Davies, the claimant was unable to evidence any further diminution in value between 2013 and 2018 so their claim for damages failed. 

In addition, in Davies, the claimant tried to argue that the residual diminution in value is the reduction in value after their neighbour treated the Japanese knotweed in 2018, because of a stigma attached to the land in the property market. However, there was nothing in the evidence which supported this proposition, and the Supreme Court did not consider that this was a good argument. 

It is therefore important to demonstrate that your neighbour’s breach of duty caused the loss suffered and evidence that there had been further diminution in value between 2013 and 2018. 

Vibuhti Parmar is an associate at Charles Russell Speechlys LLP and Aaron Walder is a barrister at Landmark Chambers.

This article was first published in Estates Gazette on 8 July 2024.