Confusingly, the male and worker Buff-tailed Bumblebees have a white or off-white tail and are easy to confuse with workers of the White-tailed Bumblebee.
Separation on these pages is mainly on the basis of the ginger/orange hue of the stripe on the upper thorax and on the abdomen being Buff-tails (White-tails being more yellow or straw).
Busy on bizzy. Note the full pollen sacs on the back leg of these busy workers.
Both the Buff-tailed and the White-tailed Bumblebees, being short-tongued species, make holes in the base of long, tubular flowers like the Russian comfrey here to reach the nectar. (These could be White-tailed Bees? But the bands seem slightly more orange.)
The orange-coloured bands are the give-away that this white-tailed bee is not a White-tailed but a Buff-tailed Bumblebee.
Buff-tailed Bumblebee face
Buff-tailed Bumblebee workers with full pollen sacs
These last three could be Buff-tailed or may be White-tailed. I'd plump for Buff-tailed for the two on the white hogweed but am uncertain about the final one on the orange flower.