I don’t know about immigration, but it is well known that the UK has very much tightened requirements for visitor/tourism in recent times. Where for decades South Africans didn’t even need a Visa, now they do, and obtaining one is expensive, time-consuming, tending to invade one’s privacy, and unpleasant in all sorts of ways (e.g. spending days in queues, etc.). Perhaps this particular case is just one typical example of several possible reasons of why the UK is doing this.

Is this another righteous pot-shot at SA?
Illegal immigration problems occur in every progressive country. It’s our one of our biggest problems.
Scum is everywhere and not an exclusively South African feature.
We have tons of British low-life scum on our soil, too – remember Maggie Thatcher’s son, Mark?
Live in Sweden, Italy, Ireland, Greece and Germany for a while. You’re in for a BIG surprise.