Access to suitable proving ground will determine the initial venues. Near to home it could be either Ecton or possibly Alderley Edge. Further afield and Rhiwbach Slate Mine is the most likely contender.

I'm hoping to be doing the biz by the forthcoming Christmas break.

Above: Me stood on the shelf over the floor opening to a lower level in Rhiwbach. I've lowered a camera and tatical LED torch down to around 30 feet (10m) Photo © Vanoord

Picture Notes
The picture above may be a little confusing. The rectangular dark block on the left which is from water level down is a continuation of the wall above and not a reflection. It then shelves and falls away. Below where I'm standing the opening appears to go in the direction of the passage that is behind me. At the bottom of the opening there is some twisted iron rubble and the floor slopes away from the camera towards me and beyond. You can see how the rays of light from the torch light up the lower level. You can see more images of the exercise taken by Vanoord HERE You can supersize the picture above by clicking on it.