Marestail

I think it’s extremely difficult to eradicate. The roots are very deep and run everywhere. Sorry no suggestions, other than covering the area so it’s starved of light, although it will return.
Digging it up will break the roots and spread it.

Yes I've been digging it up and it spread now it's everywhere! Nightmare stuff to deal with

It is the worst weed ever, I used to have it on my allotment. Treating the young growth with SBK brushwood killer, repeatedly, did get rid of it eventually, but it’s a long haul and other plot holders weren’t as diligent.

That's the trouble, ours comes in from next door under the fence as they don't care about it, its other people's that can creep

It will keep coming and coming. All you can do is to keep cutting it down or use a systematic weed killer. Eventually it may give up but it will take some time as the roots are so deep. It’s one of the oldest plants on earth.