At SE Knotweed, we explain that knotweed encroaching from a neighbour is a private nuisance question: responsibility can rest with a neighbour who knew about it and failed to act, but the position is fact-specific and needs legal advice.
At SE Knotweed, we explain that knotweed encroaching from a neighbour can be their responsibility in private nuisance, but only where they knew or ought to have known about it and failed to take reasonable steps to control it. The position turns on their knowledge and conduct.
Having knotweed is not in itself unlawful, so a neighbour is not automatically liable simply because the plant grows on their land. A survey records the source and extent, which is the evidence any claim or negotiation rests on. Take legal advice before acting.
A neighbour becomes liable when knotweed spreads from their land onto yours and they have breached a duty in private nuisance, which arises once they know or ought to know of the plant and fail to take reasonable steps to stop it interfering with your property.
Courts have treated published guidance, such as that from the RICS and the Environment Agency, as fixing the point at which a landowner ought to have known. Liability follows the breach, not merely the presence of the plant.
Private nuisance in a knotweed case is unlawful interference with your use and enjoyment of your land, made out where a neighbour's failure to control the plant lets its rhizome encroach across the boundary and burden your property.
The interference is the encroachment of the underground rhizome and the blight it places on the affected land, not just the visible canes. This is the cause of action behind an encroachment claim, and it is separate from the public-law offences under the Wildlife and Countryside Act.
You do have to show, on the balance of probabilities, that the knotweed encroached from the neighbour's land, which is where a survey earns its place: it maps the stand, records the direction of spread and identifies the likely source.
A surveyor can trace the rhizome across the boundary and read the growth from the stand's maturity. Without that evidence a claim struggles, so we record the source carefully in the report.
Where a neighbour is responsible, you can usually recover the reasonable cost of treating the encroaching knotweed and any expense caused by the interference, such as the survey fee and, in some cases, the cost of a barrier.
What you generally cannot recover is a residual fall in value once the plant is treated, a limit the Supreme Court confirmed in Davies v Bridgend. We set out the recoverable and the non-recoverable heads plainly rather than promising a payout.
Davies v Bridgend County Borough Council [2024] UKSC 15 held that a residual diminution in a property's value is not recoverable in nuisance where the encroachment happened before the defendant was in breach of any duty, which narrows what a claimant can win from a neighbour or authority.
It does not end neighbour claims: the cost of treatment and dealing with a live nuisance can still be recovered. The diminution in value page explains the decision and its limits in full.
In most cases it is worth raising the knotweed with your neighbour first, in writing, because it puts them on notice, which is often the point at which their duty in nuisance begins, and it can resolve matters without a claim.
Keep a dated record of what you send and their response. If they fail to act, a solicitor's letter is the next step, and the survey gives both the evidence. We can provide the report that supports the correspondence.
A council can serve a Community Protection Notice under the Anti-social Behaviour, Crime and Policing Act 2014 where knotweed on someone's land is having a detrimental effect on the quality of life of others, requiring the occupier to control it.
Breaching a notice is an offence and can lead to a fine, so a Community Protection Notice is a route worth raising with the local authority where a neighbour will not act. It sits alongside, not instead of, a private nuisance claim.
The evidence you need is a survey that confirms the species, maps the stand, records the direction and likely source of the encroachment, and reads the growth, together with your dated correspondence putting the neighbour on notice.
That package supports a negotiation, a Community Protection Notice request or a claim. Book a survey and we will produce a report written so a solicitor can rely on it.
Tell us the address and what a surveyor flagged. We confirm the plant, record the RICS category and set out the figures.