Thanks Colin, As regards to lighting it is a single 100cm Octabax at a 45 degree angle, the light is high up and angled at 45 degrees or thereabouts.
The model is on the very edge light (aka kissing the light), so it lights her correctly but as the light falls off onto the background it becomes darker.
I always try and get 2 stops darker on the background than the model. Distance from camera to model, model to light, light to background all play a major part.
Its the sort of set up you get right first time or not, i have had a bit frustration with this more than once.
Its a bit of a signature look for me, but i am getting a bit of tired of it. The next shoot I have i will try something different !!