What is this?

Or vicious even?

I think we get a lot of that too, whatever it is, at least the leaves look familiar, but not long roots.

Looks like it might be nan, thank you!

I think I asked about the full grown plant previously as I thought it was very pretty - wish I'd been more viscous with the damned thing!!

I wonder if it could be Enchanter's nightshade - Circaea lutetiana? Spreads by white stringy roots, I have it in my garden, and it's a pest! Every little piece of root will grow, so very difficult to eradicate.