Update from me - I got a letter from DHA yesterday saying my request for business travel from the UK to SA has been approved. I'm current in FRA having started a 10 day period here so I could fly Lufthansa to JNB, but now I'm heading back to LHR to fly BA from there (there are no direct flights from FRA to JNB until Friday).

The only concern right now is that these letters are clearly being produced manually, with passenger names been cut and paste into the letters and then saved. So my name and email address in the header are correct, as is my passport number - but it's addressed to the wrong person and in another sentence, I've been christened with an addtional name!

As comments above, online check-in is disabled, so I'm about 4 hours from presenting this document (and my negative C19 test) to BA staff. Wish me luck!