I have dual nationality ie a British and a South African passport. My British passport has expired I will be renew once in the UK. I will be travelling from South Africa, into Dublin and on to Heathrow.
Do I need a visa using my South African passport commuting from IRELAND to UK?
It depends on the airline. Some airlines require passports and if the only passport you have is South African, then you also need a visa to go with it.
However, not all transportation operators between Ireland and the UK require passports for British citizens -- several other forms of ID/documentation can also suffice. There's a (non-authoritative, possibly inaccurate) list at Wikipedia.
There shouldn't be any immigration control on arrival in London, due to the Common Travel Area.
