Yesterday I started lifting both the rediscovered path and the comfrey, both of which mark the boundary between bed 4 and 5. The comfrey then goes to the central path edge, where it should look spectacular when it grows to over a metre, and flowers.
I suspect it's Symphytum officinale (rather than one of the Bocking F1s) because it was growing randomly at the old Pig Sty Avenue, by a common path. Just the sort of place a plant would grow from a stray seed. I think regular garden comfrey is fine for composting and fertiliser, but wants watching because it's a persistent bugger, and I don't want to be invaded by even a beneficial plant. So it'll need cut down before it has a chance to set seed.
It's not all good, comfrey. It has anti-fungal qualities, which is of course a mixed blessing. It might have some effect on the chocolate spot which is infecting the winter field beans I'm growing as a crop this year, (the comfrey is growing right along the edge of their bed), but it will also inhibit mycorrhizae.