Maybe Circaea lutetiana??? The white roots would support that id. Are you sure they're seedlings and not returning perennials?

If so, I shouldn’t be pulling them to make way for pachysandra!

It's a complete pain on my allotment where any fragment sprouts but I would leave it alone if it was in woodland.

Then I'm glad that many still remain. I am trying to increase the natives, but it's so rare that I find any that I can sometimes be a bulldozer. I am so appreciative of the knowledge so generously shared here.

That's all supposing I'm right about the id.......... if it flowers you'll know.