I anticipate there will be a statement shortly on this, I don't think there is anything out yet, which means BA and other airlines are being informed at the moment. Sky News is reporting, and I'm not going to contradict, that inbound flights from South Africa to the UK will be prohibited from tonight. I will post if I see anything more, but it's going to be a busy news night.

I suspect a Statutory Instrument is about to follow too, presumably to ensure recent arrivals in the UK do self isolate regardless of exemption status, and their household members too.