Digging or glyphosate will do the brambles.
Are you talking about Japanese knotweed?
I don't think I can do better than these organisations.
How sure are you? A great number of plants have been labelled JKW on this forum over the last year. Some were, a lot weren't
Have you a photo of it in growth?
or its dead stalks
You can only follow their suggestions for eradication.
Hi Smiler, Nut is right dont go wasting money on sprays and such ,and dont cut it till you know what your doing,iv been there before and got advise from an expert ,it can take 2 to 3 years to eradicate its not too expensive, Find the sours of it and get good advise from the proper people dont start worrying and dont take advise from anyone except the experts ,much cheeper in the long run, good luck.