A landmark ruling about the invasive plant Japanese knotweed has been over-turned – with implications for landlords and other property owners. 

In February 2023, Marc Davies won a Court of Appeal case against Bridgend council in South Wales, after Japanese knotweed encroached into his property from council land. 

He was awarded £4,900 for the damage the weed did to the value of his home. Japanese Knotweed spreads rapidly, particularly in warmer weather, and has bamboo-like stems which grow to over two metres in height. They suppress other plant growth and may damage the structure of a property in the most extreme cases.

However, in this case Bridgend council appealed and the Supreme Court has now ruled that Davies is not entitled to any compensation, because the weed had been thought to exist in the owner’s property since 2013 – some years before the owner first raised the problem with the council, in 2018. 

Nic Seal – founder of invasive plant specialist consultancy Environet – says:  “The claimant is not now entitled to damages for diminution in the value of his property because the loss was deemed to have occurred prior to the Council’s breach of duty in 2013.

“But this judgement has clarified that any resultant diminution and/or remediation works necessitated after the breach of duty are recoverable.

“This judgment does not therefore mean that all future knotweed-related claims will fail, since most cases of knotweed encroachment will have occurred more recently. But it does highlight the critical importance of homeowners being alert to what is happening on adjoining land and putting a neighbouring landowner on notice where knotweed is at or near a boundary.

“With constructive knowledge of the problem, if the neighbour fails to act and encroachment occurs, then a nuisance claim including residual diminution may well succeed.

“I expect we may also see a rise in victims of encroachment demanding the method most likely to achieve eradication of knotweed, namely excavation, rather than settling for damages calculated on the sum of herbicide treatment cost and diminution, since the diminution element of their legal claim may now be less assured.”