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The prayers of homeowners whose property values are weighed down by Japanese knotweed could have been answered: a new study suggests the plant is relatively harmless. Received wisdom considers the pervasive plant to be extremely damaging to homes because its roots can crack concrete and damage foundations. Half of mortgage lenders won’t even consider loans on properties affected by knotweed. Only this week a senior Appeal Court judge ruled that neighbours could sue each other if the “pernicious weed” spreads across boundaries.

But research by the University of Leeds and engineering firm Page 3 Aecom, seen exclusively by Telegraph Money, threatens to shatter the knotweed consensus.

Despite property owners’ fears of hearing the dreaded words associated with their home, this is the first scientific study into the matter.

The report examined 68 homes where knotweed was found, as well as 81 additional sites. It also scrutinised existing research on knotweed damage and quizzed surveyors and invasive species experts.

Dr Mark Fennell of Aecom said: “We found nothing to suggest that Japanese knotweed causes significant damage to buildings – even when it is growing in close proximity – and certainly no more damage than other species that are not subject to such strict lending policies.”

Contrary to popular belief, the report found that knotweed could not grow through concrete. Its authors said this idea was “simply not supported by any evidence, as it is not possible due to the laws and principles of physics and biology”.

While knotweed can worsen existing cracks in structures, the plant prefers to grow around obstacles rather than burrow through them.

Mortgage lenders currently require action if knotweed is found within 23ft of a structure. This is due to the belief that the plant’s roots will grow far enough to damage structures within this zone. But the research found that knotweed roots normally extended up to 8ft and rarely more than 13ft.

If knotweed is too close to a house, lenders generally require sellers to pay for specialist treatment, which costs £2,000 to £5,000 for a three-bedroom semi-detached house.

The report said lenders were being overcautious when it came to knotweed. It said: “Despite the significant socio-economic impacts of such automatic mortgage option restriction, little research has been conducted to investigate this issue.”

In the short term, very little is expected to change as a result of the research. Lenders are unlikely to relax their rules around knotweed overnight and homeowners with the untreated weed will probably still struggle to find buyers who can get a mortgage.

In the longer term, however, mortgage brokers say lenders could and should relax their rules around properties with knotweed.

David Hollingworth of London & Country Mortgages said: “Lending criteria should be living and breathing, and should evolve.”

Martin Stewart of London Money, an independent mortgage adviser, said: “The words ‘Japanese knotweed’ used to turn people’s blood to cement because of the negative connotations. Now I don’t think it’s as bad as people think, and this report will help. Knotweed has a bad reputation but I’ve had two clients with it recently and the lenders were OK with it.”

Regardless of any research, public opinion around knotweed will take a while to change, meaning that

A groundbreaking study has found that the plant’s reputation as harmful may have been wrong all along, reports Sam Barker