I am planning a trip to France and other Schengen countries. First point of entry will by France. I am from South africa. Can I visit from France, with a Schengen visa from there the UK? Can I apply on that side, or do I have to apply in my own country first?
The UK is not in the Schengen Area, therefore you cannot enter the UK on a Schengen Visa. In order to enter the UK, you will need a Standard Visitor Visa for the UK, in addition to the Schengen Visa you will require to visit France.
You can apply for the Standard Visitor Visa in any country with a British "Consulate General", although I'd recommend applying ahead of time and from your home country, simply because the consulate in South Africa will have more experience with applications from South Africans, and because the process can have minor problems which are much more pleasant to resolve from the comfort of your home, months before you need to: trying to solve them from France 2 weeks before you want to enter the UK could be stressful.
You will require a Standard Visitors Visa for the UK and a Schengen Visa for France. You will need to apply for the Schengen Visa from South Africa or where you are currently resident.
You can get a Standard Visitors Visa for the UK from any country with a British Consulate General. It's best though to apply from the country where you are resident.
Source: I am a South African national.