Japanese knotweed wrongly knocking thousands off house prices because of out-of-date science used by mortgage lenders

17 May 2019

Japanese knotweed is wrongly wiping thousands off the value of properties because lenders are relying on out-of-date scientific evidence, according to an investigation by MPs.

A new report from Parliament’s Science and Technology Committee has found that that mortgage lenders are taking an “overly cautious” approach to the plant.

It says that the seven metre rule – the property line from the plant used to decide mortgages – is being used as a “blunt instrument” in some lending decisions and does not reflect the latest scientific evidence.

The report says that Japanese knotweed is no greater threat than other disruptive plants and trees that are not subject to the same controls and do not have such a substantial “chilling” effect on the sale of a property.

Also known as fallopia japonica, Japanese knotweed is a fast-growing invasive plant with bamboo-like stems.

It was first introduced to the UK in the in the mid-nineteenth century as an ornamental plant in parks and gardens but has since become a significant nuisance due to its invasive nature.

If the problem is only recognised when buyers arrange a survey it can also cause property sales to fall through.

It has been estimated that over 2% of development sites and 1.25% of residential properties in Great Britain are affected by the plant, amounting to tens of thousands of sites in total.

Mortgage lenders will usually require evidence of treatment that will eradicate the plant as a condition of lending if knotweed is present on or near a property.

“A significant industry is built around controlling Japanese knotweed. During the inquiry, the committee was told that mortgage lenders in other countries do not treat the plant with the same degree of caution,” the report says.

The report is calling for a more measured and evidence-based approach to ensure that the impact on lending decisions is proportionate to the plant’s impact.

Norman Lamb MP, chair of the Science and Technology Committee, says: “It is clear that the UK’s current approach to Japanese knotweed is more cautious than it needs to be, especially when comparing it to that of other countries.

“We need an evidence-based and nuanced approach to the issue, one that reassures owners and buyers that they will not be subject to disproportionate caution when trying to sell or buy a property.”

The report recommends that the Department for Environment, Food and Rural Affairs commissions a study of international approaches to Japanese knotweed in the context of property sales to get more information on the issue.


In reply to by anonymous_stub (not verified)

I have just lost 90,000 pounds on my house because of 1 stem of japanese knotweed. it is a 100 year old site and the demand is that i have to identify where it came from. How would I know? Instead of 320,000 my house is no up for auction for 230,000. Is this right? The plant is rife in Devon and you cannot tell if people cut it down before putting their house on the market. The house foundation are set deep in bedrock and the knotweed is over by the gate - perhaps it is under the road - how would anyone know? So my 4 bedroom house with a third of an acre of land has been completely smashed by one stupid plant that cannot affect the house at all. That is not a 10% reduction as was said in another of your posts, it is a heck of a lot more. Now i will be homeless as a result.

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