Described by the Environment Agency as 'indisputably the UK's most aggressive, destructive and invasive plant', Japanese Knotweed (Fallopia japonica) was originally introduced to the UK in the 1850s as an ornamental plant and animal feed. It has spread rapidly and estimates now suggest at least one infestation in every 10 square kilometres across the UK. Knotweed can grow 3-4 metres in a 10 week growing season, and as little as 0.7 grams of rhizome (roots) can produce a new plant within 10 days. The rhizomes can spread to a depth of 3 metres, and 7 metres horizontally.  This strong growth and invasive root system can damage concrete foundations, buildings, roads, paving and retaining walls.

Though it is not an offence to have Knotweed on your land, and it is not a notifiable weed, under the Wildlife and Countryside Act 1981 it is a criminal offence, with a potentially unlimited fine and/or up to two years imprisonment, to plant Knotweed or otherwise cause it to grow in the wild. In the case of corporate bodies, such penalties can be imposed on an officer of the company if the offence was committed with that person's consent or neglect. It is a defence to a prosecution to prove that all reasonable steps were taken and all due diligence was exercised.

Under the Environment Protection Act 1990, Knotweed is 'controlled waste' and must be disposed of in accordance with the proper procedures, including the Environmental Protection (Duty of Care) Regulations 1991. Further, as treatment of Knotweed involves the application of herbicides, the Control of Substances Hazardous to Health Regulations 2002 must be followed. In some cases, as when chemicals are used in or near a watercourse, the Environment Agency must be informed (The Food and Environment Protection Act 1985 and The Control of Pesticides Regulations 1986).