Can anyone help me identify the plant below? I've got a patch of it growing in our new (overgrown) allotment, and it looks as if it was planted on purpose. I would like to know what it is before I dig it all up as a weed.
It's got really deep gnarly white roots (this one snapped). I was thinking perhaps horseradish? If it is I'll keep some, although there's far too much there at the moment!