Moving on from arguments, because it's usually so lovely and supportive here
Slip, you mentionned having phoned several agencies, so you may have found them already, but have you approached OASIS or the IAC? They have good advice on intercountry adoption, and if they can't help you with the South Africa bit, they can certainly tell you all about the UK side of it, the homestudy etc
I don't actually know much about SA, but I don't believe there are any adoptions taking place between the UK and SA. A quick search brought up a page saying that the D of E were only approving relative adoptions, and that there hadn't been the necessary review yet to approve any others. The review was supposed to happen 2010, but hadn't happened by 2011 either. You could approach the D of E and ask them whether you can adopt from SA maybe?
I think if you are allowed, you should be prepared to be quite alone in doing so I'm afraid- this doesn't seem an option for anyone who thinks they would need hand-holding or lots of help, because there is so little information. You would be finding out all the information by yourself, without any previous adopters to tell you what you need to do and when.So nothing like the domestic process where it's very clear what happens and when. Bearing in mind how stressful adoption can be, are you happy to be very on your own with the process in South Africa? Happy to approach organisations alone and deal with them? Happy for the process to take quite a while, because countries which barely process any international adoptions rarely have people with experience, so the process can take much longer because no one is 100% sure of what they're doing the first few times around.
Also, this is purely out of interest, but if South Africa does not work out are you interested in domestic adoption or other countries?
Sorry I can't help any more. Good luck