What you Need to Know about Civil Law and Japanese Knotweed

Japanese knotweed civil law suits are becoming ever more common. With that commonality there often arises truths, mistruths and half-truths.

Whether you are considering making a claim, or having to defend a claim, here is an overview of what you need to know – Whether you are a homeowner or neighbour to a Japanese knotwood problem.

Our Managing Director Nic Seal CEnv, MIEMA, BSc, is recognised as a leading expert in the field of Japanese knotweed, and as such is often called upon as an experienced Japanese knotweed expert witness. Here he takes a look at how this affects the home owner and neighbouring areas.

Nic writes:

The most common civil law cases relating to knotweed can be summarised in 3 main areas:

Private Nuisance/Encroachment

Private nuisance/Encroachment occurs when the Japanese knotweed spreads from one parcel of land to another.

Prior to any claim the aggrieved owner should seek to resolve the issue with their neighbour in an amicable way. This will involve co-operation between neighbours, perhaps agreeing to a combined treatment programme on a shared cost basis.

If this fails, the aggrieved neighbour should seek legal advice to determine whether they have a case against the landowner of the neighbouring land. If so, the advice is likely to be for the claimant to notify the neighbouring landowner (the defendant) of the nuisance to give them reasonable time to put mitigation measures in place. If that fails to illicit any action, then legal action is probably the only way forward. However, before one embarks on such a course, one must weigh up the costs of litigation, the risks involved, the chance of success, and the effect on future neighbour relations.

In order to bring a successful claim, a claimant needs to be able to prove on the balance of probabilities that the knotweed originated from the defendant’s land. It will be necessary to prove that the encroachment is causing the claimant nuisance resulting in tangible losses. The outcome of a successful claim is likely to be a monetary award to the value of those losses incurred.

The claimant’s solicitor will almost certainly need an expert report from a knotweed specialist to give opinion on the source, and quantum of cost for treatment or removal. Where diminution (i.e. reduction) in property value is also being claimed then an expert report from a valuation surveyor experienced in knotweed cases will also be required. The claimant’s solicitor will build the case, and issue a “letter before action” designed to bring the defendant to the negotiating table, to try and resolve the case prior to court proceedings.

The defendant would be advised to get his/her own legal representation. They may decide to obtain their own expert reports, or decide to instruct joint experts with the claimants to reduce professional costs, and avoid lengthy and expensive disagreements between experts.

One common defence is that all reasonable mitigation measures have been put in place by the defendant, leaving the debate to what is meant by “reasonable”. The judgment against Network Rail in February 2017 in favour of two homeowners whose properties were affected by knotweed on Network Rail land strengthens the case for claimants able to prove an actionable nuisance.


Misrepresentation occurs when the seller does not declare that Japanese knotweed is present on the property.

During the conveyancing process, sellers are obliged to complete pre-contract enquiries, usually following the Law Society’s standard TA6 form. Question 7 of the form asks “Is the property affected by Japanese knotweed?” giving the seller the choice of “Yes”, “No” or “Not known” as answers. The seller must answer this question truthfully, having made due enquiry, or face the risk of a misrepresentation claim. Many unsuspecting buyers of residential property find in their first spring or summer of ownership new shoots of a fast growing plant, later to be identified as the dreaded Japanese knotweed.

If you are unlucky enough to be one, check what answer was given by the seller on the TA6 form. Speak to a solicitor who is experienced in misrepresentation claims. A “Not known” answer does not necessarily get the seller off the hook. Speak to your new neighbours; they may be able to provide evidence to prove the seller knew of the knotweed presence. Likewise, if you are in contact with the seller’s gardeners, ask them.

A “No” answer can be interpreted to be categorical and will be harder for the seller to defend. There can be intentional or innocent misrepresentation. For example, knotweed could have been treated many years previously making the seller honestly believe the property is not affected anymore. The Courts will deal with an innocent misrepresentation more favourably.

If it’s a “Yes” you probably don’t have a claim against the seller. But if you weren’t advised that the knotweed would represent a problem you may wish to consider whether your conveyancing solicitor has been negligent in his duty to you.

In a misrepresentation case the damages are likely to be calculated on the basis of the cost of treatment with a solid insurance backed guarantee, and the reduction in value that a willing buyer and willing seller would have agreed both in the knowledge that the knotweed was present.

Professional Negligence

Professional negligence occurs when Surveyors fail to identify Japanese knotweed.

The most common professional negligence cases are where a surveyor has failed to identify and report the presence of knotweed on a property. The defence is usually that the knotweed was not obvious at the time of the survey; possibly because of the time of year, or that the knotweed had been concealed, whether intentionally or not. The difficulty in proving the case therefore hinges on being able to get evidence that proves the knotweed was present at the time of the survey.

Sometimes photographic evidence is available. Occasionally, the surveyor scores an “own goal”, including a photo in their report showing the knotweed. In other cases the buyer or even estate agent may have taken photos which may help to prove the case.

A professional negligence claim will normally be managed by the surveyor’s PI insurers, who will take a more commercial approach, and either decide to fight the claim or settle quickly.

If you have had a claim made against you, or are the victim of encroachment, misrepresentation or professional negligence then please do not hesitate to call us today on 01932 868 700 to find out how we can help you.

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