Japanese knotweed is an invasive, non-native weed that has been present in the UK since the 1850s. Excavation of Japanese knotweed can be extremely difficult and costly and its invasive root system has the potential to undermine built structures.

Japanese knotweed has had adverse effects on property values. Mortgage lenders often require evidence that a ‘treatment programme’ is in place to control and remove Japanese knotweed which incurs significant expense for homeowners and potential buyers.

Desktop surveys do not usually reveal the presence of knotweed; specialist invasive weed professionals often need to be instructed (on behalf of either the homeowner or a prospective buyer) to advise on necessary steps and the likely costs of a containment programme.

How is it treated under the law?

Whilst it is not illegal to have Japanese knotweed on your property in the UK, ignoring an order to control it is a criminal offence.

Japanese knotweed is classified as ‘controlled waste’ and dug-out soil contaminated with its roots or seeds must be disposed of safely under the Environmental Protection Act 1990. Offenders face unlimited fines, with current Home Office guidance recommending penalties of around £2,500 for individuals and £20,000 for organisations. It is likely that liability for costs incurred in disposing of the soil/plant incorrectly would also be imposed.

Finance and Insurance

Lenders and insurance companies are usually reluctant to offer services relating to Japanese knotweed-contaminated land without evidence of some sort of specialist mitigation plan. The majority of these eradication service products are designed to meet the demands of insurance companies, banks and building societies.

Buildings insurance policies do not generally cover damage or problems caused by Japanese knotweed. Some companies that offer treatment plans will include ongoing guarantees to cover the cost of any re-growing Japanese knotweed; these can be backed by insurance in case the original eradication provider ceases to operate.

Recent Court Decision

In Williams and Another v Network Rail Infrastructure Ltd 2017, homeowners of two adjoining bungalows in Wales made a claim against Network Rail, who owned a rail embankment behind their properties. Japanese knotweed had been present on the embankment for approximately 50 years. The Claimants argued that:

(1) the knotweed roots had encroached upon their property up to the foundations although no damage had been caused; and

(2) the knotweed’s effect on the value of their property interfered with the quiet enjoyment/amenity value.

The Court held that damage was required to prove loss under encroachment, but the fact that mortgage lenders refused to provide even limited mortgages on properties where Japanese knotweed was within seven metres of the boundary without evidence of a treatment plan in place, was sufficient to prove diminution of value.

The Claimants were awarded damages of £14,320 each to cover diminution in value and the cost of a treatment plan, plus £350 per year for loss of amenity. This case will be of interest to homeowners and their lenders seeking damages to cover the significant expense of multi-year treatment programmes and loss of value.

Please note that this information is provided for general knowledge only and therefore specific advice should be sought for individual cases.

For further information, please contact John Mills