Adam Smith and Eleanor Smith v Rosemary Line (February 2018)
Following a trial in October 2017, the Truro County Court recently delivered judgment on a case concerning the spread of Japanese knotweed. Adam and Eleanor Smith asserted that their neighbour Rosemary Line allowed Japanese knotweed to spread from her land onto their adjoining property, worth £500,000, and as a result was responsible for a devaluation of their home of £50,000.
Japanese knotweed is an invasive non-native species (INNS), known by the scientific term Fallopia japonica. This plant can negatively impact the amenity of an area, and its extensive root system can cause physical damage to buildings and land, thus its presence can significantly reduce the value of a property, its marketability and its insurability. Furthermore, its rapid growth rate and extreme durability mean that it is difficult to contain. The law, therefore, seeks to prevent the spreading of this invasive species of plant.
Japanese knotweed is listed in Part II of Schedule 9 to the Wildlife and Countryside Act 1981 and is subject to section 14(2) of this Act, meaning any person who plants it or causes it to spread – in other words, knowingly allows it to spread without taking reasonable measures to contain it – is guilty of an offence. In addition, any owner of occupier of land who allows an INNS plan to spread onto neighbouring land could now be found liable in common law nuisance. This has become apparent in the 2017 decision in Williams v Network Rail Infrastructure Ltd  UK CC, and the recent decision of Smith v Line. In the latter case, the court held that Rosemary Line was liable in common law nuisance for a 10% diminution in value of the Smiths’ property because she permitted Japanese knotweed to spread from her land onto theirs.
It should be noted that the Williams v Network Rail case is being appealed.