So at JNB checkin this morning .. initial refusal , no checkin on separate tickets .. but then decided it was possible as long as it was OneWorld after consulting with the colleague in QR uniform on the next desk ... I was checked in on the BA app .. much furious keyboard bashing ensued and eventually got the bags tagged through to London and boarding cards for the BA connection issued .. I think what made it slower was that she was trying to check the bags in for the BA flight number on the same date, not tomorrow and that obviously wasn't going to work .. Anyway got there in the end

The only slight issue was that she said the system was trying to charge me for the second bag ( though the Boarding card she printed out did have my status on it ) .. didn't matter as just put the second bag on under one of the other passengers on the booking