It is true, many sales have fallen through as a result of Japanese Knotweed and lending policies.
Japanese Knotweed should not prevent a house sale being completed; it just adds a few steps in the process if everyone is open and there is a mutual understanding backed by a professional report and treatment service.
Once the Knotweed is controlled with a suitable insurance backed guarantee, mortgage providers and others will usually lend. It all very much depends on the individual site; the level of the Japanese Knotweed that is present and where it has come from and many other factors which are assessed on a house-by-house basis.
It is always best to contact us and get the Japanese Knotweed verified and ascertain where it is coming from and who is responsible for it, and what your options are.