As SztupY mentioned, you need to request permission retain your South African citizenship on gaining any other citizenship. If you are not granted such permission, you will lose South African citizenship.
I am a little worried you may have lost your South African citizenship on gaining Polish citizenship.
If you are in the UK / London, the process for retaining citizenship is detailed on the South Africa House Citizenship Retention Page.
I suggest you apply in person, since finding someone to certify a copy of your passport according to South African standards is likely to be expensive / difficult.
You should leave a good few weeks for this process before you gain UK citizenship, since the first step could take more than 2 weeks.
- Apply for a letter confirming you have not gained British Citizenship from the UK government. This currently (March 2014) costs £94, and will take 10 working days.
- Download and fill in the BI-1664 and BI-529 forms from the South Africa House page (more details about which items to cross out and ignore are on the same page). If you have questions, staff at South Africa House are helpful. Print a couple of spare copies in case you have forgotten something.
- Make a couple of copies of the photo page of your passport. Don't forget this, or you will need to find a photocopier somewhere in central London. South Africa House staff won't do it for you.
- Draw £25 in cash for the South Africa House fee (current price as at March 2014)
- Visit the Consular Section of South Africa House at 15 Whitehall, London, SW1A 2DD in person. No appointment is necessary, but you should arrive from 08:45 to 12:45 Monday to Friday (note that this excludes South African public holidays, which UK consular staff take as holidays).
Expect the process to take a few hours. If all is well, you should leave with the appropriate permission letter on the same day.