It is considered an offence to cause Japanese knotweed to be spread from one site to another. If the invasive knotweed is found on a site boundary, crossing into adjoining properties, then it is often the case that the origin of the Japanese knotweed is unknown and that responsibility for the Japanese knotweed control may be shared.

In the Wildlife and Countryside Act 1981, knotweed is listed in Schedule 9, Section 14. It is an offence to actively plant or otherwise cause the species to grow in the wild. But it is not actually illegal to have it on your land, nor is there any specific law against allowing it to spread, although doing so could be a nuisance.

In the Environmental Protection Act 1990, Japanese knotweed is classed as ‘controlled waste’ and must be disposed of safely at a licensed facility according to the Environmental Protection Act (Duty of Care) Regulations 1991. Soil containing the rhizomes of the plant can be regarded as contaminated and, if taken off a site, must be disposed of at a suitably licensed facility. At landfill sites, the waste due to Japanese knotweed removal must be buried to a depth of at least 5 meters.

If the area of infestation in question is not to be disturbed or built upon at any time in the near future, then the Japanese knotweed can often be treated with a specific herbicide that will be part of a Japanese knotweed eradication strategy.

This will involve the spraying of the invasive plant with herbicide for several years, until there has been no re-growth for at least two years. It is important to remember that in the United Kingdom spraying of Japanese knotweed carried out near water, requires the permission of the Environment Agency; this is obtained with form WQM1. Japanese knotweed herbicide spraying near or in water will require the use of a non persistent herbicide such as glyphosate. This type of herbicide will break down quickly in contact with the soil, microbes and water. If no watercourses or groundwater are nearby, then it may be possible to use a more persistent herbicide such as Tordon 22k (picloram) in order to treat the Japanese knotweed growth.
Japanese knotweed hindering construction works or obstructing water-ways can be treated through excavation. Excavation of Japanese knotweed is more costly than the control of Japanese knotweed through herbicide use, but the use of excavation to control the spread of Japanese knotweed is a more immediate solution to the problems posed by Japanese knotweed.