The frame was a design originated by BSA during WW2 to provide the British Army with instant transport for its Airborne forces after landing by parachute; the bikes had hinges half way along the top and down tubes so it folded in half, together with 'collapsible' pedals which pushed through the cranks. Just bought another nice original one
For value though you need to post in the 'whats my "X" worth' thread