Japanese knotweed and Himalayan balsam were introduced into the UK as ornamental plants. However, they are extremely invasive and have taken over large areas of habitat, reducing the success of native floral species.
Under Schedule 9 of the Wildlife and Countryside Act (WCA) 1981 (as amended) it is an offence 'to plant or otherwise encourage' the growth of Japanese knotweed or Himalayan balsam in the wild. With Japanese knotweed this includes cutting the plant or roots and disturbing surrounding soil if not correctly managed. Soil within 7m of a stand of Japanese knotweed can contain its rhizomes and therefore, specific mitigation will be required for any work within 7m of any stands of Japanese knotweed that are identified.