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Japanese Knotweed – A Legal Update

The dangers of Japanese Knotweed have again recently hit the headlines. Knotweed can prove a nightmare for property owners and neighbours, as the plant is able to grow up to 10cm a day, with the roots extending 3m deep and 7m wide. The Government also officially recognises it as an invasive plant.

History of Japanese Knotweed

Japanese Knotweed is native to Japan, China and parts of Korea and Taiwan. It was first introduced to the United Kingdom in 1825, by German Botanist Phillipp Franz Von Siebold, to cultivate and sell as an ornamental plant to the wealthy classes.

Japanese Knotweed arrived in London’s Kew Gardens in 1850. The plant had been in Great Britain for more than 155 years before it was recognised as an invasive plant by the Government and, by this time, it had already been distributed to garden nurseries throughout the UK.

Japanese Knotweed is now common in the UK and can be found growing along canals, near railway lines and motorways but it is also found in residential gardens and near commercial property. It is understood that the parts of the UK most affected by this plant are the Bolton, Bristol and Nottingham areas.

Why should you be concerned?

When Japanese Knotweed is found on a property it can cause serious issues.

It is an invasive species of plant which is difficult to manage and eradicate - and the control and management of it can be extremely costly and it can take up to 5 years to properly treat.

  • It may physically damage your property – it is strong enough to break through concrete;
  • The property may be difficult to sell and mortgage (its presence would need to be disclosed to any potential buyer and/or lender);
  • The value of the property may be negatively affected (reportedly by 5-15% although in some cases it can make a property completely unmortgage able); and
  • it may affect any plans for development.

Japanese Knotweed often has extensive subterranean rhizomes (an underground network of plant stems) and this needs drastic remedial measures to remove, which may result in the entire top soil of the property being removed and disposed of as hazardous waste.  

Recent Case Law - Davies v Bridgend County Borough Council (2023)

A recent decision by the Court of Appeal has allowed a homeowner to claim compensation after Japanese Knotweed spread from a nearby cycle path owned by the Local Authority to the claimant’s garden.

Although the Local Authority had carried out a treatment programme to attempt to remove the plant from the site, it was found that there had been encroachment of rhizomes on the claimant’s property and therefore, physical interference with the claimant’s property had occurred. Consequential losses, including diminution in value, were recoverable even after treatment of the property.

The key element to note in this decision is that the Court of Appeal held that there had to be physical damage and/or interference with the claimant’s property in order for there to be an actionable nuisance. It is reported that this case cost the Local Authority £300,000 in legal costs and the damages for ‘residual diminution’ recovered by Mr Davies was in the region of £4,900.

Recent Case Law – Downing v Henderson (2023)

Jonathan Downing successfully sued the seller of a house in Southwest London for misrepresenting that there was no Japanese Knotweed at the property. The seller had answered “no” to the question on the Property Information Form asking if the property had ever been affected by Knotweed. But when the buyer moved in, he found Knotweed in the back garden.

The buyer claimed he couldn’t see the Knotweed due to a large bush, but it had previously stood 2m tall and there was evidence it had been previously treated.

The seller’s defence was dismissed, and the Judge ruled in the buyer’s favour. Mr Henderson was ordered to pay damaged of £32,000 and costs of £95,000 for misrepresentation.

This case highlights the important of only answering “no” to the presence of Japanese Knotweed if you are certain there is none.

Any issues with Japanese Knotweed should be disclosed to a buyer. Otherwise, the buyer should be asked to rely on their own inspection.




These notes have been prepared for the purpose of articles only. They should not be regarded as a substitute for taking legal advice.

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