My memory is that the Liberals were the mainstream party most associated with the anti Apartheid movement at that time? Although there were plenty of worthies from Labour willing to turn-out and lend some degree of support/raise their profile at rallies/events.
Most of the South African kids I met in that period were from families who had got-out just because of what the country had become under Apartheid - There were plenty working in oil/engineering here at the time. Which was in marked contrast to the ex-Rhodesians who arrived in the same period who all seemed so full of bitter hatred for what ”the Blacks/Communists” had done to “their” country. Most of them went away pretty quickly though.
I’m also remembering that although not segregated, people of British or “other European” heritage were kept legally at a lower level in South African society under the Apartheid regime, which put those of Boer/Dutch heritage firmly at the top.