structure on bramble leaf, presumably containing an insect?
No interactions present.
A Common Slug
it was attached to the bramble leaf and standing up, not fallen down.
The cases are mobile, as each contains a caterpillar. They can also be blown/knocked off their food plant and in one instance I have seen them descending from a tree on silk threads. The attaching phase is, I think, the point at which the larva undergoes metamorphosis and will later "hatch" as a moth.
Lat/Lng: 51.9591, -0.638948
OS grid ref: SP936298