When travelling between points that only BA serves in Africa and Europe....when originating in Africa (assume SEZ), your itin must be something like the following if you needed a stop in EUR:

Assuming only BA serves MCT and SEZ

SEZ-LHR first LHR arrival
LHR-MCT
MCT-LHR second LHR arrival
LHR-HKG
HKG-JFK
JFK-LHR third LHR arrival
LHR-SEZ

Without going through London 3 times, you are limited to the cities that you can go to.