Perenniel weed may be a knotweed

Japanese Knotweed does flower when it reaches about 4' in height, small white fringe-like flowers. The new shoots are red and like a small spear when they emerge. The stems arch over, is this what yours is doing? It also grows very quickly, almost as you are looking at it!!! if you have got it, it's extremely difficult to get rid of - we never did eradicate it completely from our previous garden. Repeated doses of Glyphosate helped to keep it down, but as you say, the roots are very deep.

Thanks very much. Thought that would be the olnly way. Will start at once