Thank you Charles. I do dig them out, including their root but somehow more appear and when we came back after 2 weeks away the ground was covered. I just hoped that there might be an easier method of dealing with them. However I have found out that they are bi annual so maybe getting them out before they seed is the thing to do.
If it was just around the edges they could stay & I know that bull finches love them & actually I love them along our riverbank – just not thousands on them on the allotment.
Incidentally your advice on brambles has worked a treat. We now just dig as much as possible out and cut the root off as far down as we can and we only occasionally get any regrowth and that seems to pull out easily. Or at least it did before the un composted areas cracked up in the drought.