In article , Janet Baraclough
writes

Any chance of a picture of it Janet?

Not only is Bocking 14 sterile, it doesn't spread by runners, and is
also one of the largest forms of comfrey (at least 3ft tall with huge
leaves). I've grown it for decades and it stays right where its planted,
producing massive crops which I harvest all summer for mulch, making
compost, and making liquid fertiliser.
--
Judith Lea