I can confirm that this was indeed for stretcher cases. Sometime about 1970 I accompanied a patient from Oldchurch Hospital Romford to Edinburgh. My mother was the almoner at the hospital. Ambulance to Kings Cross, then boarded the overnight train using the hinged window arrangement. Well the stretcher went in that way. Met at Edinburgh by an ambulance crew to convey the patient to hospital. He was a roofer who lived in Galashiels, but had fallen off/through a roof while working in the Romford area. Kicked my heels around Edinburgh for a few hours then on the 10am service back.Although the body was alive in this case. On some BR standard compartment stock a compartment facing the corridor external door had a window where the large lower half was hinged. I was told this was for stretched cases. Was this correct and if so was it ever used for that purpose?