Any foreign aid the UK can throw into SA is dwarfed by that which China (a country that is also best buddies with Argentina) is pouring into the country.
If you've got some data on China's foreign aid to SA (and indeed to anywhere else) you'd better get in touch with the FCO - I'm sure they'd be interested. China does not publish details of its foreign assistance.
China does, however, very actively pursue large infrastructure programs in Africa and other developing countries. They are able to substantially under-bid most Western companies, and often combine this with low interest loans. As a result, China's influence in the third world and Africa particularly has grown very significantly since the end of the Cold War. This strategy of gaining influence around the world is more far-sighted than trying to impose globally impose military might. One wonders what the USA might have achieved if part of their enormous military budget had been used in this way.