Hi Peter. I believe councils with this problem are using high strength weedkillers now with good results, but I don't know what tactics they're using with them. My ex husband lives next door to a wooded area and it was coming through into the garden so they are now addressing it. I expect they've done it over the summer and will look at it in spring when growth gets going again. If I can remember to ask him more about it I will.
The weedkiller is injected into the stem after it has been cut, it has to be growing.
Thanks Fairygirl and Fleurisa.