Japanese knotweed chokes £41m a year from UK economy

Japanese knotweed costs Britain £41 million a year, a study has found, as experts call for more investment to stop future invasive species reaching the UK.

The nightmarish plant was introduced to the UK more than 150 years ago and is notorious for its ability to cause significant structural damage and being extremely difficult to kill.

Dr Ross Cuthbert of Queen’s University Belfast led a project to analyse the economic impact of all the UK’s invasive species, and found that since 1975, they have accounted for at least a £5.4 billion hit to the economy.

However, a lack of reliable data means this figure is best viewed as a baseline, and the true value could be “an order of magnitude” higher.

The majority of the costs have been incurred in the past 10 years, and a handful of species make up the bulk of the damage.

European rabbits, brought to the UK by the Normans a millennium ago, are the most costly invasive species, the study found, causing £165 million of damage every year since 2010.

Japanese knotweed is second, at £41 million a year, followed by the rock pigeon (£29 million), floating pennywort (£6.3 million), and the brown rat (£5.7 million).

“The majority of [Japanese knotweed’s] economical impact is in house devaluation from when you have knotweed on the property, and also the cost of removing an infestation,” Dr Cuthbert told The Telegraph.

“I hope the publication of this paper will spur on future research and increase awareness of invasive species which have well-known environmental impacts, but also have economic effects. Politicians and decision makers understand money, they don't understand ecology.”

Nic Seal, founder and managing director of Environet UK, an invasive plant removal specialist firm, told The Telegraph: “Control of invasive species with blunt regulation is extremely complex and notoriously difficult to enforce.

“Other interventions, such as mortgage lending policies by banks as in the case of Japanese knotweed, and general awareness of the environmental problems these species cause, is likely to have far more impact.”