Japanese knotweed and private nuisance

16 July 2021

Jonathan Pennington Legh acted recently in a case concerning Japanese knotweed. Here he considers how the related legislation impacts landowners and practical steps you may like to consider.

More claims likely

As Japanese knotweed appears to be becoming more prevalent, more claims brought against neighbouring landowners are probable.

Local authorities or other bodies (eg railway companies) are most likely to be defending such claims, because the source of Japanese knotweed is often unoccupied or waste land – the ownership of which they retain.

These claims will be in private nuisance.

Knotty issue of Japanese knotweed

The presence of Japanese knotweed on a property (or even within 7 metres of it) is a substantial problem. It can have a massive impact on the property’s value even before it does any actual physical damage to it.

Significantly for property owners, it can affect the ability to remortgage.

This invasive plant is incredibly difficult to remove properly and completely. Realistically it can only be done by experts at substantial (often a five figure) cost. Indeed most mortgage providers will require expert removal and the 5 or 10 year guarantee that the specialists provide.

The landowner would be well advised to seek advice as soon as possible, and not themselves to take any steps to dig it out, poison it or even build over the Japanese knotweed.

See the government’s Prevent Japanese knotweed from spreading guidance.

Japanese knotweed and the law

Landowners who have identified Japanese knotweed on their land and fail to act to stop it spreading onto someone else’s property could face criminal proceedings and a fine of up to £5,000.

The leading recent case is Williams v Network Rail Infrastructure Ltd [2018] EWCA Civ 1514, [2018] 3 WLR 1105 which amongst other things established that the mere presence of Japanese knotweed or its rhizomes on land interfered with the land’s amenity value without proof of further damage.

This is because it imposed an immediate burden on the landowner by way of an increased difficulty to develop and the cost of developing the land should the owner wish to do so. Consequently there was no need to prove actual or imminent physical harm.

Therefore damages can be substantial – as well as the cost of remediation there may be a diminution in value (which could be as high as 10% of the value and may even exist even after the remediation) and general damages. The court in Williams awarded £350 per year for the latter.

Aside from legal claims, Japanese knotweed and its problems will be well known to conveyancers (a question about Japanese knotweed is specifically asked on the SPIF) and the insurance market.

If you would like any advice on bringing or defending a claim relating to Japanese knotweed, please contact me or my clerks.