Japanese knotweed has been described as ‘a real thug’ by the Royal Horticultural Society and there is no denying that it is the bully of the plant world.
It destroys other native species, grows voraciously and can force itself through concrete causing damage to buildings and infrastructure.
It is expensive and time-consuming to eradicate completely. As a result, its presence on or in the vicinity of a property can stop lenders from providing finance to potential purchasers.
Even following a treatment programme, affected properties are likely to suffer from a residual diminution in value.
Williams v Network Rail Infrastructure Ltd  UK CC before Cardiff County Court involved a claim for damages by residential landowners in private nuisance against NRIL on the basis that knotweed had encroached into their land from a railway embankment at the rear of their properties.
Additionally, the landowners claimed that the mere presence of knotweed in close proximity to their properties was an actionable interference with the enjoyment of their land because they could not sell their properties at a proper value.
The claimants failed in their action for encroachment because of the lack of evidence of physical damage to the properties. They were however successful in claiming that the mere presence of knotweed in close proximity to their properties was an actionable interference with the enjoyment of their land.
NRIL argued that landowners can only bring successful nuisance claims where there is physical damage to the land or an interruption to the enjoyment of the use of their land. In cases of physical damage to land, the measure of damages would be the diminution in the value of the land and, in cases of an interruption in enjoyment, the measure would be the reduction in amenity value.
In NRIL’s opinion, a loss in market value of the property does not stem from any physical damage, nor does it interrupt the enjoyment of the land. The county court dismissed NRIL’s arguments.
The judge said that ‘the right to use and dispose of a residential property at a market value is… so important a part of an ordinary householder’s enjoyment of his property’ that an interference with this right would result in a reduction in the amenity value of the property.
Occupiers have a duty to take such steps as are reasonable to prevent or minimise dangers to adjoining land from natural hazards on their land where they have actual or constructive knowledge of the nuisance.
The court decided that NRIL knew about the presence of the knotweed and the potential risk of harm to neighbouring properties but it had failed to take reasonable steps to prevent or minimise the potential damage.
While the knotweed appears to have been present for 50 years, NRIL’s submission of a prescriptive right defence failed because there was no proof of knowledge and acceptance that the nuisance had continued for at least 20 years.
Another reason this case is significant is that the defendant was deemed as having constructive knowledge of the potential impact of knotweed due to the publication, in 2012-2013, of RICS and the Property Care Association guides, which highlighted the damage that Japanese knotweed can do to property, property values and insurance. This publication predated actual knowledge of the nuisance, which was established as when the claimants notified NRIL of the presence of Japanese knotweed.
The damages awarded to each claimant were comprised of a treatment programme and insurance backed guarantee; miscellaneous loss; general damages and, particularly significantly, a residual diminution of the claimant’s property.
In this case, evidentially, there was around a 10% diminution in the property’s value. Although a county court judgment, this highlights the potentially very serious repercussions if, for example, a large number of high value properties were affected, and has particular implications for large landowners attempting to control invasive non-native species particularly along railway lines, highways and rivers.
This case could lead to such landowners paying out significant sums in compensation following this decision. Time will tell whether or not NRIL takes action to appeal the county court’s decision.
Photo by Matt From London