Japanese knotweed can grow at the rate of 10cm a day during the summer, is extremely difficult to eradicate and can make a property unsaleable. To make matters worse, research indicates that very few people are readily able to identify Japanese knotweed; property owners therefore need to be alive to the risks that it can create.
Schedule 9 to the Wildlife and Countryside Act 1981 [WCA 1981] lists certain plants that have become established in the wild in Great Britain, but which the law seeks to prevent spreading further. This includes Japanese knotweed that is categorised as an Invasive Non-Native Species, otherwise referred to as an INNS.
The presence of Japanese knotweed can give rise to common law nuisance where it involves an unlawful interference with the use and enjoyment of another's land and results in loss of enjoyment or amenity and property damage. Nuisance can be caused by inaction or omission as well as by positive activity. An occupier will be liable for failing to act reasonably to remove the Japanese knotweed after becoming aware of it and where it was foreseeable that it would damage a neighbour’s land.
What’s more, Japanese knotweed can also give rise to criminal penalties. The WCA 1981creates various offences including making a person guilty of an offence if they plant or otherwise cause to grow an INNS. Negligent or reckless behaviour, such as inappropriate disposal of garden waste resulting in an INNS becoming established in the wild, would also constitute as an offence.
Accordingly, if an owner or occupier of land fails to control Japanese knotweed or allows it to spread onto neighbouring land, this may give rise to costly claims for loss of enjoyment or amenity, the cost of removal and potential criminal sanctions.
In the recent Court of Appeal decision in the case of Network Rail Infrastructure Limited v Williams and Another  EWCA Civ 1514 on 3 July 2018, the Court of Appeal held that the mere presence of Japanese knotweed can be an actionable nuisance, even before it causes physical damage to the neighbouring land. In other words, a property owner is likely to be granted an injunction requiring a neighbour to control knotweed on his or her land on the basis of anticipatory damage.
This is likely to be of particular concern to land owners of public land, railways, roads and rivers and the like, who may have Japanese knotweed on their property near boundaries.
Standard residential enquiries specifically ask about the presence of Japanese knotweed and accordingly, sellers need to be very careful in their replies. A seller who does not occupy or who has not inspected the property, may well reply that the buyer should rely on his or her own inspection and survey. However, if the seller replies ‘not so far as the seller is aware’, without making reasonable efforts to check for the presence of Japanese knotweed, the seller risks being found liable for misrepresentation.