It spreads prolifically through its underground rhizome system, overwhelming everything in its path, damaging the foundations, drainage systems and walls of properties, proving almost impossible to remove without a sustained eradication programme carried out by specialists. Clearing the plant from the London Olympic site cost more than £70 million.

Legal implications

The presence of Japanese Knotweed can have legal implications and consequences for neighbours, landlords, tenant, buyers and sellers of land and houses. Local authorities have powers under the Town and Country Planning Act 1990 to require landowners to remedy the condition of land, and failure to comply can result in prosecution, a fine and the awarding of the costs of undertaking the removal work.

Local authorities or the police can potentially serve community protection notices under the Anti-Social Behaviour Crime and Policing Act 2014 for failure to keep an alien plant under control. In addition, landowners could face criminal liability under the Wildlife and Countryside Act 1981 for allowing the escape of the plant. Knotweed disposal is taken very seriously; it’s classed as controlled waste and must be disposed of properly; failure to do so could result in liability for breach of procedures.

Knotweed and property valuations

For all of these reasons, its presence can lower the real or perceived value of a property. Lenders may be reluctant to advance mortgages on land where they know the weed is present, and may insist on you hiring a professional firm to eradicate it before granting the loan; it’s not generally covered under building insurance policies either.

If you’re buying a property in an area where the weed has been identified, pre-contract enquiries should address the issue, but if in doubt, we’d recommend asking the question specifically. If you’re selling and you’re asked specifically about the presence of knotweed, then our advice would be that you ask the purchaser to make their own inspection, rather than relying on a response of ‘not as far as the Seller is aware’ as this could leave you liable for misrepresentation if you don’t confirm the position first.

If you’re a property owner and have the misfortune of an infestation, ensure that any removal work is carried out by a specialist firm and covered by guarantee which can be assigned to subsequent purchasers.