Morning Antony,
I started my flying training back in 2009, and did a very similar route to what you're looking at. I completed my PPL and hour building in South Africa, whilst doing Bristol Ground School's distance learning ATPL. Then, once you've built your hours, you can return to the UK to complete a small amount of Multi-engine and instrument training to the complete a UK CPL/ME/IR. Once you complete your UK ATPL exams, you then have a frozen ATPL.
Once you have your SA PPL, you can use it to fly privately in the UK. All you'll need is a check flight, and you're good to go.
Flying in SA is amazing, and with the exchange rate at the moment, it'll save you a lot of cash. Only problem is the schools there aren't really affiliated with any airlines etc, so wont be able to help you out getting a job at the end.
I training at 43 air school - just down the road from Algoa. I don't know much about the air school itself, but PE is a good airport to be based at.
Hope that helps.