Are we overly cautious when dealing with Japanese knotweed? Are other countries more proportionate in their approach? And do we need a new risk assessment to better reflect the situation on the ground? Read on to find out what the government’s Select Committee has concluded in an area where policy looks set to change …

In December 2018 we blogged on the UK Science and Technology Commons Select Committee’s plan to consult on “the science behind the effects of Japanese knotweed on the built environment”. The Select Committee was keen to obtain evidence surrounding the practical impact that the presence of knotweed has on buying and lending decisions in the UK and, more importantly, the reasoning behind those decisions. The results are in and the overriding conclusion is that we need to change our approach, but more evidence is needed before a revised policy framework can be set to deal with knotweed affected land.

So what did the Select Committee actually conclude following its consultation? Despite the fact that other plants cause a similar level of physical damage to property as Japanese knotweed, the stigma attached to the latter in the UK means that the reaction to its presence (as evidenced by property valuations) is often over-exaggerated. The only feature of Japanese knotweed which could potentially explain this excessive stigma is that it is more difficult to completely eradicate than other invasive plants. Despite this, the general consensus is that the UK’s approach to knotweed is “overly cautious” compared with other European countries.

Our colleagues in Germany, for example, report that knotweed is simply not a hot topic. They tell us the approach there is a pragmatic one – due to costs, landlords rather than tenants are responsible for its removal. There is also a “self-help” remedy available if a neighbour allows knotweed to encroach on your land, allowing you to remove it and be compensated appropriately.

Similarly in Hungary Japanese knotweed does not seem to have a major influence on buying or lending decisions. Anyone who allows knotweed to grow and spread may be fined and required to eradicate it. If the person responsible can’t be identified, the owner, tenant or manager of the property is obliged to deal with it. But our colleagues tell us it is not a hot topic or an issue in the same way as it continues to be in the UK.

In France the approach is even more “hands off”. There are certain non-native species of plants which cannot be introduced into the environment. However, Japanese knotweed doesn’t even make it onto the list. It is not considered as an invasive alien species and can be planted in France. There are certain rules on environmental practice which state that farmers mustn’t plant it near watercourses, but that’s about it.

So is our approach “overly cautious” compared to our European neighbours? Should this be rectified and if so, how? This is proving difficult to agree. The Royal Institution of Chartered Surveyors (RICS) risk assessment from 2012 is credited with improving lenders’ attitude to properties affected by Japanese knotweed – many lenders simply refused to lend at all in such circumstances prior to the risk assessment’s publication.

That being said, some of the standards set in the risk assessment have been widely criticised as arbitrary. The “seven metre rule” (i.e. if knotweed is visible within a seven metre radius of any building or the property boundary, then the property is deemed higher risk) which is one of the key tenets of the risk assessment, is not based on scientific evidence.

As a result, many commentators have demanded a more nuanced approach to risk classification. Such classification should take into account: the size of the infestation, the distance of the knotweed from the property and the type of property (among other factors). This plea for an amended risk assessment is currently being considered by RICS but any revised content has not yet been settled.

In general, it’s been agreed that more evidence is needed:

(a) to establish the physical effects of Japanese knotweed on the built environment; and

(b) on the way in which Japanese knotweed is treated in other jurisdictions.

Such evidence is needed to inform future policy and regulation so that it is both proportionate and rational.

The UK government’s Select Committee has tasked the Environment Agency, the Department for Environment Food & Rural Affairs and RICS (among others) with investigating the issues set out above.