As people have said pouring very very strong weedkiller into the stem of the thick ones is the best bet. My neighbour has this and it was brought up on my house inspection 2 1/2 years ago. No problems with halifax giving me a mortage. I guess because its not in my garden. Some of it has of course encroached but i have a cheeky fence panel that opens so i can check on the otehr guys garden (its huge and weirdly shaped so he’ll never seeme, oh and hes about 120 years old.)
I’ve found that if you want to kill the smaller stems off when they first start growing a little bit of white spirit will kill it in about 4 hours. I have no idea how effective it is below the surface but I seem to be winning the war slowly…
JK is a serious thing. So much so it is a criminal offence to handle it incorrectly or NOT treat it if its on your property. The damage it does is insane and yes it really does grow a foot in a week as per the above post. In fact in last years hot rain showers i’m sure some of my neighborus grew more than that. probably 18 inches plus shoots from the side and big big leaves. Crazystuff.
edit: as you cant control whats on the railway embankment i wouldnt even bother going near the property.