Invasive knotweeds are some of the most pernicious invasive plants across the world, with Japanese knotweed being the most common and problematic knotweed within the UK, having been introduced in the mid-1900s as an ornamental plant. Japanese knotweed is not listed in the EU List of Invasive Alien Species of Union concern since there is insufficient evidence that it meets the listing criteria (Reg. No. 1143/2014, 2014). However, the UK has legislation surrounding Japanese knotweed, and more generally, invasive species (e.g. relating to its release and disposal of waste). In the context of residential property sales, knotweed should be declared during the conveyancing process when a TA6 form is completed. A TA6 form, which includes questions regarding Japanese knotweed, is used for residential property but not commercial property sales. It is applicable in England and Wales within the Law Society’s Conveyancing Quality Scheme. Whilst most conveyancers adopt this scheme, it is not compulsory. 

The report found that there is a link between the question on Japanese knotweed on the TA6 property information form and the policies of lenders, as informed by advice from the surveyors and valuers upon whom they rely. This link is now backed up by case law as well as the statutory framework. The TA6 question on Japanese knotweed was the result of policies adopted by lending institutions - the continued use of the question is due to current lending policies as reinforced by existing and emerging case law.

This, in turn, informs the advice provided by surveyors and valuers to lending institutions and expert evidence given in court proceedings on matters relating to Japanese knotweed. The evidence collected for this study suggests that the UK approach to knotweed in property sales is not disproportionate given the level of invasion of knotweed and the control measures that may be required where knotweed is present, if only to enable householders to use their gardens and outside space. 

The report can be found here on Defra's ScienceSearch portal, or be downloaded here.