They are beetle pupae, probably weevils, almost certainly vine weevil, Otiorhynchus sulcatus.
They are a a serious pest. The larvae love feeding on the roots of pot plants, and on the roots of many plants in the garden, especially sedum and sempervivum in my experience. The adults chew chunks out of the edges of leaves (less of a problem).
I cannot be 100% sure they are vine weevil, because
"Other related species that have recently become established in Britain, such as Otiorhynchus armadillo, O. crataegi and O. salicicola, cause similar damage to foliage."