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South Africans are visa exempt for Ireland for 3 months.
However, if connecting in the UK on the way there, they have to clear UK immigration as Ireland is in the CTA.
The GOV.UK website states the following regarding South Africans going to Ireland via the UK:
You’ll usually need to apply for a UK standard visitor visa;
You might be eligible for ‘transit without visa’ if [...] [you] have the right documents for your destination (for example a visa for that country)
You must also have an Irish biometric visa (marked ‘BC’ or ‘BC BIVS’ in the ‘Remarks’ section) and an onward flight ticket to the Republic of Ireland.
The second and third statements overlap but differ: the second statement implies you just need to have the right papers to enter Ireland (for a South African, a passport), while the third statement specifically says you need an Irish visa to connect the UK visa-free.
Judging by the first and third statements combined, it would appear that a South African, despite being visa exempt for Ireland, would need either a UK Standard visitor visa or an Irish visa if connecting in the UK.
Is this the case?