What is this weed and how can I get rid of it permanently?

This may work or not with this, but I am reminded of when I had a polytunnel erected on a very rough neglected field.

The garden centre who did the work told me not to try to dig but to put thick layers ( plural) of cardboard, then manure and grow i n that.

Great crops and a year later I saw that the roots of any weeds that had survived including reeds, had risen to the surface to try to find light and freedon and were easy to lift out carefully.

The nettles were like spaghetti ...never saw another there

I would never use poison.