The white, tubular flowers are very attractive to bumblebees and must be nectar rich. This picture was taken on 5th April and the plant had been in flower for well over a month, helping the bumbles to get off to a good start.
Most species of comfrey have had many medical applications in the past, but these are best avoided as plants in the Symphytum genus have been shown to be somewhat toxic.
We also have a colony of Hidcote comfrey, S. x hidcotense, with blue and white flowers but the same creeping habit. I think this must have been the plant Kenneth Grahame wrote about in Wind-in-the-Willows: "Comfrey, the purple hand-in-hand with the white, crept forth to take its place in the line."
