how can south africans live in thwe uk legally after their visa has run out?

Answer 1

It would be necessary to apply for another visa or in order to stay long term an application for citizenship or ILS (Indefinite Leave to Stay) would have to be submitted.

Such applications should be made through the British High Commission in Pretpria http://www.britain.org.za/ or the Foreign and Commonwealth Office in London http://www.fco.gov.uk