To add that for many years BA used to shuttle their 747 s on to Gaborone or Durban, returning to JNB for the evening flight back to LHR (even Cape Town was a 747 shuttle in the distant past until that got a dedicated LHR-CPT service). Unfortunately the onward loads to DUR or GBE were not good enough to make the shuttles economically viable and so they were withdrawn a few years back.