Normally these charges and requirements are reciprocal so it is possible that the UK may introduce a charge.
As it is my compatriots (fortunately I have an EU passport) have to pay R816 for a short term visa or nearly R3000 for a 2 year one to visit the UK, whereas UK citizens do not pay for a holiday visa to SA. There is also the time involved, it's all a bit aggravating but it's the fault of our own Department of Home Affairs who allowed criminals to get ther filthy hands on blank passports which were then issued to non-South Africans.