Hi Mike,
I think you're talking about the weedy oxalis that I get in my garden a lot. I just pull it out when I see it. It has a small tap root, so I wonder if you're just cutting part of the root and leaving enough for the plant to return.
Remy

Dear Remy. Many thanks. At least you`ve identified the enemy ! Since I posted the query, OXALIS continues to appear, especially in the dahlia beds. I`ll try pulling instead of cutting and see if that works. It attacks every empty space between plants, generating itself literally in days; and I get at least a shovel full each time I go round the beds. May have to resign myself to accepting it is here to stay.
Grateful for your interestand prompt reply. Best Mike