Yes indeed it seems that two pages are no longer necessary (since they stopped using the sticker visas around 18 months ago ) for entry to SA ... however it seems that some airlines still enforce the 2 page rule, indeed some insist apparently on 2 consecutive pages (opposite eachother) being free

Timatic says it's only one page needed now .. and the info presented on BA.com confirms this .. so hopefully the Passport & Visa check guys agree !

I wonder also if it's a bit different for transit via JNB ?

Annoyingly (but perhaps unsurprisingly) the rules seem a bit ambiguous for Namibia too and very much open to the whims of what border staff do on the day ! .. Hopefully BA are only checking for one free page (if checking that at all) when they do the Docs check at LHR before departure.