Japanese Knotweed was introduced to the United Kingdom from Japan in 1825 as an ornamental plant. Without the pests and diseases that control it in Japan, it grows and spreads rapidly in “non-native” Europe and the USA, displacing native flora and causing structural damage. It is now a serious problem in a range of habitats, particularly roadsides, riverbanks and derelict land. Not only does the presence of Japanese Knotweed carry certain legal implications for the landowner, but its existence impacts on the value of a property and the ability for the landowner to obtain funding and insurance. 

Laws relating to Japanese Knotweed

It is not against the law to have Japanese Knotweed on your land. However Section 14 of the Wildlife and Countryside Act 1981 makes it an offence to plant or otherwise cause knotweed to grow in the wild. (It is generally thought that private land and in particular gardens do not come within the definition of “wild”). 

Knotweed is classed as “controlled waste” under The Environmental Protection Act 1990 and any plant material and/or knotweed contaminated soil must be disposed of in accordance with the requirements of the 1990 Act, at appropriately licenced landfills. Failure to comply with the 1990 Act requirements can result in prosecution. The Environment Agency has published the “Knotweed Code of Practice” which, although aimed at development sites, contains guidance applicable to all landowners. Guidance is also published by the Scottish Environment Protection Agency (SEPA).

As between private landowners, where knotweed moves from one parcel of land to another, the law of “private nuisance” may apply. The owner of knotweed affected land would be advised to take reasonable steps to abate the nuisance, following the Environment Agency’s Guidance, to assist in defending any claim brought by an adjoining landowner for nuisance. It should be noted that because nuisance is a legal tort, damages does not extend to pure economic loss. Therefore it is likely that loss of development value could not be claimed.

Knotweed liability may also apply to the tenant of land, depending on the lease wording and whether the knotweed was present at the time the lease was granted.

RICS Japanese Knotweed and Residential Information Paper

The RICS issued its information paper on Japanese Knotweed in March 2012. Although it considers the implications of knotweed infestation on or near a residential dwelling, when undertaking valuations and surveys, many of the issues highlighted will affect commercial properties as well.

The following points are noteworthy:


  • Neither the Council of Mortgage Lenders nor the Building Societies Association have published a formal policy on the issue, but on consulting their members it was clear that there is a general reluctance to lend on properties affected by knotweed.
  • Lenders may be willing to consider applications on a case by case basis once remediation works have been implemented and subject to borrowers agreeing to fund a three to four year treatment programme.


  • Most buildings insurance policies do not cover loss or damage caused by knotweed, therefore the land owner will have to fund any remediation and repair works out of its own resources.
  • Insurance cover may not be available for properties affected by knotweed. This will affect mortgageability.

Scale of the problem and impact on value

  • There is a perception that the scale of the problem has been exaggerated. The RICS estimates the cost of rectifying “serious” damage to a residential property would be £15,413 plus VAT as at December 2011. Most infestations are not serious and can be controlled at a manageable cost. Cases of extreme damage to buildings by knotweed are rare.
  • The RICS suggest that by quantifying the likely cost of treatment and necessary repairs, the impact of the presence of knotweed can be treated like any other defect or want of disrepair in the valuation process and that where knotweed is present in the ground but has caused no damage to the property itself this may have no adverse impact on value.
  • However, in our view this may be a simplistic approach, bearing in mind that it can take more than three years to be certain that some of the treatments have been effective, and this would undoubtedly affect the saleability of a property. 

Environment Agency – the Knotweed Code of Practice for development sites

The Environment Agency has issued a code of practice on managing knotweed on development sites. The guidance contains useful information on the treatment, prevention of spreading and disposal of knotweed and soil contaminated with knotweed.

The guidance indicates that the presence of knotweed should not prevent a developer from buying a site, but the cost remediation will impact on his appraisal. Other factors to consider are whether it is possible to treat the material on site and the on-going costs of managing the knotweed post remediation.

Considerations when buying a property

  • Check whether the property is situated in an area where Japanese knotweed infestations are common or near to features associated with the growth of knotweed such as local water sources, public and private paths and cycle paths, roads, railway embankments, large open spaces, commercial/industrial buildings. Some local authorities have dedicated “Knotweed” pages on their websites.
  • Always commission a home buyer report or a building survey – this will involve an inspection of the property and its grounds. Where the features noted above are present ensure that an inspection over and along the boundaries is also carried out.
  • Ask the seller and his solicitors to confirm whether the property or any adjoining property has been affected by Japanese knotweed.
  • Where a property has been treated for knotweed infestation, check whether the works have been guaranteed and whether the company providing the guarantee remains solvent.

What to do if you think your property maybe infested with knotweed

  • Contact the local authority – many have useful information on their websites.
  • Contact RICS – they may able to refer you to a surveyor with specialist knowledge.
  • Speak to the Environment Agency (SEPA in Scotland) – they can provide advice on disposing of “waste”.
  • Notify your insurers.
  • Notify your lender. 

To read the Environment Agency's Code of Practice for knotweed click here.