I grew up on a farm in SA and spent most of my time outdoors and Ive adapted just fine to the UK weather. Its not that bad considering parts of SA also have pretty cappy weather.
The "parts of SA that have crappy weather" you refer to, I assume is Cape Town, which has crappy weather only in winter, which is 3 months long. Winter in London is 9 months long, constant crappy weather. And there are many summers that go by where the sun hardly shone, like 2007's summer.