Bee nest in a window frame

Bee nest in a window frame

Observation - Bee nest in a window frame - UK and Ireland. Description: I opened a window that had been closed since last summer and found these pupal cases that seem to contain pollen. There was a bee buzzing around too, which may or may not be associated with this nest. It was about the size of a honey bee, but had a browne

I opened a window that had been closed since last summer and found these pupal cases that seem to contain pollen. There was a bee buzzing around too, which may or may not be associated with this nest. It was about the size of a honey bee, but had a browner thorax. Couldn't get a photo, unfortunately.
No idea what the insect that made these was, but there is a lot of pollen in the pupal cases. I wonder whether they are old cases being used by another species, perhaps. Any ideas, folks?