A few years ago, I was surveying a large victorian building in South London, and in the car park, the knotweed had actually cracked and heaved up a large area of concrete paving, as well as knocking a boundary wall sideways by several degrees! It was around the time when the problems were becoming even more noticeable!
There was also a wide stretch about a hundred yards long beside the A21, but that must have been treated, as you don't notice it now!
It's supposed to be quite good to eat, but I think I'll give that one a miss...
It really is evil stuff!
