Following on from the photo of the Bagworm I posted a few days ago I now think it's Adela reaumurella. Looking through MOGBI at the library today, the size, shape and construction of the case looks most likely for this species IMHO.
Also, browsing this excellent German site:
The larva looks spot on. It's not a total surprise as this is a fairly common species in oak woodland.
Still, my larva is still alive and I will try and rear it through.