In order to pass the credit checks, you need to be a UK resident to apply for a UK credit card with a UK residential address. Even then there are no guarantees that all card issuers will accept you application because you haven't yet been resident in the UK for at least six months. Try applying for a Vanquis Abacus Card or Capital One Classic who specialise in providing credit cards to those with low credit scores. Alternatively apply for a prepaid card and top it up with funds from your South African credit card or cash.