In the long run, even stronger anti-South African opinion in Britain?
There wasn't OTL
very strong anti-SA opinion in the UK because of apartheid, outside of politicians and academics, unions etc. (Remember, SA wasn't doing anything that Australia wasn't doing to it's aboriginal population prior to the late 1960s/early 1970s.)
I could see them being neutral, but with volunteers from among the white British population there enlisting, much as with Ireland, but if an Afrikaaner extremist clique had sided with the Axis I think they'd have been civil disorder if not outright civil war between the whites. And it'd have made a tasty diversionary operation during 1940/41 for the British to send troops in to remove the administration (having the support of the British SAs, many other whites and the coloureds and blacks).