My black male large garden bumblebee Bombus ruderatus from Dungeness has been sent to Paul Williams at the Natural History Museum who has confirmed that it matches the description of the species. It’s travels are not over though as it is going to be sent to China with other specimens as part of a project to analyse the DNA of this whole group of rather confusing bees.
Here is a photo of the face of this insect. Note the long face (a feature shared in common with the related small garden bumblebee Bombus hortorum) and the ginger hairs on the lower mandible - said to be a characteristic of the males of this species. They are black in hortorum, which also does not appear to come in all-black forms.