Japanese knotweed has long been recognised as a fast-growing and intrusive weed that is difficult to eradicate.
A paper on the topic published by the RICS in 2012 states that Japanese knotweed can grow, in no time, to a height of over two metres and its roots can extend up to seven metres horizontally and three metres vertically. The paper continues that it can block drains, grow between slabs of concrete, disrupt brickwork and undermine walls. Japanese knotweed is also designated “controlled waste” by the Environmental Protection Act 1990 and can only be removed and disposed of by those licensed to do so.
Clearly, the presence or proximity of Japanese knotweed has serious implications for landowners and affects the value of a property and the ability to sell or mortgage it. But is it an actionable nuisance if located on adjoining land?
This is what the court was asked to decide in Network Rail Infrastructure Ltd v Stephen Williams and Robin Waistell  EWCA Civ 1514. Japanese knotweed had knowingly been allowed to grow on land and was found to have encroached onto adjoining properties but (as yet) had caused no physical damage. The owners of the adjoining properties brought claims in private nuisance.
The Court of Appeal explained that a private nuisance is a violation of real property rights, involving either an interference with the legal rights of an owner of land or an interference with the amenity of the land – that is, the right to use and enjoy it. When Japanese knotweed is present, the risk of future physical damage to structures, the adverse effect on the ability to develop land and the expense of removing it, all affect a landowner’s ability to fully use and enjoy their land. This was a classic example of an interference with the amenity value of land.
The court therefore concluded that, in this case, the encroachment of the knotweed, even without actual physical damage, diminished the utility and amenity of the adjoining owners’ properties and they were entitled to claim damages for nuisance.
Regarded by many as a test case, this decision may well open the floodgates. Landowners who know they have knotweed on their land cannot afford to be complacent.