Thank you, yes I have tried that, the question I was asking is more specific to dealing with Network Rail on this issue. Legally I need to prove negligence which is difficult as they claim to be spraying and I cannot prove they haven't. The only thing that suggests to me that they haven't is that the knotweed continues to spread despite their advice that spraying would stunt the growth. I'm wondering if anybody has had any success in proving negligence? Sorry I should have been more specific in my initial post.