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A knotty issue: what should I do if I find one of the ‘world’s worst invasive species’ on my land?

With a place on the World Conservation Union’s list of ‘100 of the World’s Worst Invasive Species’, Japanese Knotweed is not a plant that property owners want to find on their land.

Japanese Knotweed can grow up to 2m in 30 days, can sprout from very small sections of plant (called ‘rhizomes’) and is extremely difficult to eradicate completely. One of the biggest concerns for property owners is the plant’s ability to force its way through concrete and tarmac, potentially causing damage to buildings and walls.


In the case of Network Rail Infrastructure Ltd v Williams and another, Japanese Knotweed had spread from Network Rail’s land onto the claimants’ land, but no physical damage had actually been caused to their properties. The court was asked to consider whether the mere presence of Japanese Knotweed on the claimants’ land was enough to be able to claim damages from National Rail in a claim for private nuisance.

The decision

At first, it was decided it was enough. National Rail could be held liable for the claimants’ impaired ability to sell their properties at market value due to the presence of the plant. In addition, National Rail had failed to take reasonable steps to prevent the spread of the knotweed and so the claim succeeded.

The appeal

National Rail appealed the decision and the Court of Appeal upheld the claimants’ case but on different grounds. The Court of Appeal held that a claim cannot be brought in private nuisance on the basis that a landowner’s ability to sell their property at market value has been affected.

Nevertheless, the Court of Appeal decided that the mere presence of the plant on the claimants’ properties interfered with the amenity value of their properties due to the financial burden imposed in order to remove it. The claimants could not develop their properties, should they wish to do so, without incurring significant costs. It was possible to bring a claim due to this interference with the amenity value of the claimants’ land and the appeal was consequently dismissed.

Action points for landowners and developers

Prior to the case, there was a legal duty for landowners to ensure that Japanese Knotweed couldn’t escape onto their neighbours’ land. This ruling has highlighted how neighbours can claim for damages even when no physical damage is caused to their property.

National Rail’s failure to take reasonable steps to prevent the spread of the knotweed was one of the key reasons the claim succeeded. Landowners should seek professional guidance and do all they can to ensure that knotweed does not spread to neighbouring land.

It is also worth noting that allowing Japanese Knotweed to spread into the wild is a criminal offence. The plant must only be disposed of at specialist waste carriers, ideally with professional support.

In this case, a separate but highly relevant issue for developers and landowners was also mentioned.

There are a number of different treatment methods available for Japanese Knotweed with various types of guarantee and warranty obtainable from the treatment companies. Lenders will lend on properties with a history of Japanese Knotweed, but their general attitudes and requirements vary. For example, if the plant is found within seven metres of the property, Barclays will require a 10-year insurance backed guarantee, while Nationwide requires a five-year insurance backed warranty. Anyone seeking to develop land affected by Japanese Knotweed should therefore ensure that the guarantees and treatment they obtain from the treatment company will satisfy most lenders before undertaking any treatment programme.

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Autumn 2018