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Knotty Problem

Monday, Jul-22, 2024

Knotty Problem

McCormicks’ Property team is practiced in dealing with all kinds of issues but one, in particular, has proved a challenge for both residential and commercial property owners and buyers.

Japanese knotweed is notorious for its fast growth, through its underground roots or rhizomes. It is also notorious for the lengths and expense required to eradicate it. Recent scientific studies now even question whether it can in fact ever be truly eradicated.

Knotweed can block drains, grow between slabs of concrete drives, disrupt brick paving, undermine garden walls, and overwhelm outbuildings and conservatories.

It is something that all owners and prospective developers of property of whatever type (residential and commercial) need to be aware of and vigilant for at all times, including on your own land and land in the immediate vicinity of your own.

In important developments in the law over the last two years, Network Rail (one of largest land owners in the country) has been found to be in breach of duty for causing a continuing nuisance and damage to parties who owned property adjacent to Network Rail Land on which Japanese knotweed was present.

The Court of Appeal decision in the Network Rail case is a major warning to developers and owners to ensure that any Japanese knotweed they find on their land is treated appropriately. If Japanese knotweed spreads, a developer could be liable for their neighbours' costs for dealing with the knotweed and a reduction in the value of their neighbours' land even if the neighbours’ land or property on it has not actually been damaged in any meaningful way.

The controversial aspect of the recent Court of Appeal ruling is this. The court ruled that physical damage was not necessary to give rise to an actionable nuisance. The Court of Appeal found that there did not need to be a reduction in the value of the two neighbours' properties from the knotweed. Only the "mere presence" of knotweed was required on the neighbours' land to give rise to a court claim. This presence had made that land more difficult to develop and increased the risk of future damage from the knotweed.

Network Rail was aware of the Japanese knotweed and its impacts and failed to reasonably prevent it spreading on to its neighbours' land. The court found that its treatment plan was inadequate and such findings are more likely given the new evidence coming to light about the onerous treatment levels which might be required to control if not eradicate infestations. This misunderstanding of what is required is a regrettably common occurrence in our experience.

Network Rail had to pay the costs for treating the knotweed and the reduction in the value of the neighbours' properties. Such reductions can range from three per cent to approximately ten per cent of full market value and so can be very significant sums of money indeed. We have seen five figure damages sums payable in multiple cases.

Appropriate due diligence enquiries should be raised to check if Japanese knotweed is present on any site you intend to purchase or develop. However, knotweed may be on a neighbouring site instead, and a site visit by a specialist surveyor may be required, particularly at sites that are higher risk.

If you find that Japanese knotweed is present on land in which you have an interest or are thinking of acquiring an interest, make sure your treatment plan is carried out by a specialist company which provides an insurance-backed transferable guarantee that the Japanese knotweed will not return within a minimum of 10 years from treatment. The treatment company must obtain all the necessary permits for treating and disposing of the knotweed. Further information for treating knotweed is available from the Environment Agency website.

The message from the courts is clear: Japanese knotweed must be treated appropriately or there will be legal consequences.

Our dispute resolution team has recently settled multiple cases in this area on favourable terms. We work alongside leading scientists and horticulturalists in this field and are well placed to assist with queries of any kind in this area.

If you have any concerns about this issue, please contact Philip Edmondson, Heather Roberts, Will Bates or Kim Stockburn for early advice.


Philip Edmondson


Heather Roberts

Will Bates

Kim Stockburn

Kim Stockburn


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