I've only got a few square yards to hack out with the grubbing hoe, now. There was a buried concrete structure, maybe a path once, next to the old greenhouse foundation. I leave it be: the experience has been, if there's a path of some sort, the laying of it will have been seen as an opportunity to hide glass and rubble beneath it. In fact I gave up yesterday when I came across a glass mine, always an unwelcome discovery. And something like very crumbly asphalt, though what purpose that ever served, I can't say.
Another few days should see it done. Then I have the path to lay - plenty of bricks for the purpose - from the old greenhouse area to the S boundary, and at last the path will extend the whole length of the plot, and the whole W bed will be cultivable.