Japanese knotweed has knocked £20bn off the total value of the UK property market, according to new research, with many mortgage lenders refusing loans for properties affected by the weed. Research carried out by YouGov plc on behalf on Environet, shows that approximately 900,000 (5%) UK households are affected by the weed, which the Environment Agency describes as one of the ‘most aggressive, destructive and invasive plants’. It seems the problem is growing, literally. "Japanese knotweed is the problem that just keeps growing. For most people in the UK, their home is their biggest asset and often the ‘pot of gold’ they are relying on in retirement, but Japanese knotweed is having a serious impact on values by deterring buyers and making homes difficult to sell, even if the knotweed has been successfully treated”, said Nic Seal, founder and manager of Environet. Environet have found a reduction in value, once a treatment programme with an insurance backed guarantee is in place, is between 2 and 10%. Mortgage lenders will usually refuse to advance loans unless a treatment programme is in place. Sellers are also now required to inform future buyers whether the property is or has been affected by Japanese knotweed even if it the plant has been removed. With 25% of the UK adult population having never heard of Japanese knotweed, how accurate will this information be? Mr Seal said that anyone affected by knotweed should try to resolve the problem as quickly as possible, with professional help. He warned: "DIY attempts at treatment will usually only make things worse and can even hasten the spread of the plant.” Japanese knotweed also appeared in several high profile legal cases this year, as landowners were successfully sued for allowing the plant to spread into neighbouring properties. Mark Montaldo of Knotweed Help (Cobley’s Solicitors), who specialises in Japanese knotweed litigations said: "In legal cases relating to diminution in value due to knotweed, we typically see claims for around 10 per cent of the property’s value. This is due to the stigma attached to knotweed impacting its future sale price.” We can now arrange After the Event Insurance for Japanese Knotweed claims so if you operate in this field, do get in touch, to find out more about our ClaimSafe After the Event Insurance for Japanese Knotweed claims.