Once I had removed the front sections from the box the full depth of the nest could be seen:

I managed to take it out in one piece.
Notice how the materials used start coarse and gets finer as it nears completion:

I had hoped to see some remnants of the bumblebee nest but when I parted the construction all that could be noticed was a greasy, waxy coating to the materials. That surprised me as there had been plenty of bee activity with frequent comings and goings for several weeks.
Anyway, the nestbox is empty and clean once again ready for a new occupant.