Back in the 707 VC10 days I belie this was quite a complex exercise to get the plane and crews in the right place at the right time. I believe but am not certain that on the VC 10 it was a LHR-HKG aircraft that went on from HK to Japan and then flew back down the rout e described to Jo Burg and back to HK where it was inserted back into the LHR -HK schedule. As someone mentioned I think it only operated two days per week and the crews slipped in Sez on the southern leg and then operated a SEZ-JNG and return had another layover and then returned to HK. HK-Japan was another there and back shuttle.
I am reasonable sure about this as I was lucky enough to meet up with a BOAC Steward who was part of a crew I met up with n the mid east a couple of years earlier and helped them survive a dreary layover in Qatar though use of my car and access to alcohol. I found myself promptly moved up front on the HK London section and had a very nice trip for the period that crew was on board. During that period he told me he had been n the run down to Joburg and had enjoyed several nice days in the Seychelles Of course in those days there would have been a couple or more stops between LHR and HK.
I also had a friend who was 707 pilot who told me it was a popular trip being quite a long one with nice layovers in interesting laces and a break from some f the more routine trips he did across the Atlantic
Not 100% sure of the facts but I think I am partly right and it was a truly unusual if not unique and wonderfully romantic sounding air link. Over time I managed to get to all the places it called at except Colombo but never used the actual route itself.
PB