This is a very collectible (and wearable) vintage 70s silver lame halter neck floor length dress with side slit, by UK design label, Radley.
Radley is most famous for its collections created by Ossie Clark but its own designs are just as dramatic.
This dress is shot on a UK10 mannequin and while the label states it is a UK10, I would say it would fit a UK8 person now.
It is unlined and fastens at the back with the original zip.